Damos las gracias a Stephan Wilkens para la ayuda en la microscopía electrónica de transmisión. Este trabajo fue financiado por los Institutos Nacionales de la concesión R01AG023731 Salud.

Estudios previos han demostrado que los primeros amino-terminal de 22 residuos de Mgm101 se escinden después de la importación en mitocondrias 19. Para la expresión en Escherichia coli, el marco de lectura abierto MGM101 carece de los primeros 22 codones se amplifica por PCR y se coloca aguas abajo de la secuencia de malE que codifica la proteína de unión a maltosa (MBP) en una versión modificada del vector de expresión pMAL-c2E. Esto genera la fusión MBP-Mgm101 con un enlazador que contiene un sitio de escisión para la proteasa PreScission (Figura 3). El plásmido se construyó por primera vez por la selección de E. transformantes de E. coli sin IPTG y selección azul / blanco Xgal. El plásmido pMAL-c2E-MGM101 resultante se introduce luego en la E. coli cepa BL21-CodonPlus (DE3)-RIL mediante la selección de colonias resistentes a la ampicilina y cloranfenicol. 1. Expresión, Inducción, lisis celular y DNasa I tratamiento <ol><li> INOCular transformantes frescos en 10 ml de medio LB (1% de Bacto triptona, extracto de levadura al 0,5%, 1% de NaCl) suplementado con glucosa (0,2%), ampicilina (100 mg / ml) y cloranfenicol (50 mg / ml). Incubar a 37 ° CO / N con agitación a 200 rpm. </li><li> Inocular el precultivo 10 ml en 2 litros del medio LB suplementado como anteriormente. Cultivar las células a 37 ° C con agitación hasta una DO600 alcanza 0,5. </li><li> Inducir la expresión de la proteína de fusión MBP-Mgm101 mediante la adición de isopropil β-D-1-tiogalactopiranósido (IPTG) a una concentración final de 0,3 mM. Cultivar las células con agitación a 30 ° C durante 5 h. </li><li> Recoger las células por centrifugación usando un JA-10 rotor Beckman (5500 xg, 4 ° C, 10 min). Después de desechar el sobrenadante, resuspender el sedimento celular en 30 ml de tampón de lisis (20 mM de Tris-HCl, pH 7,4 y EDTA 1 mM, pH 7,4) que contiene inhibidores de la proteasa (leupeptina 25 mM, pepstatina A 1 mM y PMSF 1 mM). </li><li> Someter a ultrasonidos suspensión de células en hielo durante 20seg usando un procesador ultrasónico (Heat Systems, Modelo W-385) en el ciclo de trabajo del 50%, se deja enfriar en hielo durante 30 seg, y repetir 2x. </li><li> Añadir 1 ml de DNAsa 1 stock a 2 mg / ml. Oscilar el lisado de células a 4 ° C durante 2 horas. </li><li> Ajuste de NaCl a una concentración final de 500 mM. </li><li> Eliminar los restos celulares por centrifugación a 10.000 xg a 4 ° C durante 30 min. </li></ol> 2. La purificación con cromatografía de afinidad de amilosa <ol><li> Equilibrar 1,5 ml de resina de amilosa (50% suspensión) en el tampón de lisis. Añadir la resina de amilosa equilibrada para el lisado de células. Agite suavemente a 4 º CO / N. </li><li> Cargar la mezcla de lisado-resina en una columna de cromatografía de columna Econo-instalado en una habitación fría. Permita que las proteínas no unidas a pasar la columna por gravedad. </li><li> Lavar la resina de amilosa con 300 ml del tampón de lavado I (20 mM de Tris-HCl, pH 7,4; 400 mM de NaCl, 1 mM de EDTA, pH 7,4, y 0,2 mM PMSF). </li><li> Repetir el lavado con 150 ml de tampón de lavado II (20 mM de Tris-HCl, pH 7,4; NaCl 200 mM, EDTA 1 mM, pH 7,4, y 0,2 mM PMSF). </li><li> Añadir 5 ml de tampón de elución (20 mM de Tris-HCl, pH 7,4, 200 mM de NaCl, 1 mM de EDTA, pH 7,4, y 0,2 mM de PMSF, 10 mM de maltosa) a la columna, incubar a 4 ° C durante 10 min, recoger el efluente y repita para más veces. </li><li> Combinar los eluatos, determinar el rendimiento y la pureza de MBP-Mgm101 mediante la carga de una parte alícuota del eluido en un gel de SDS-PAGE seguido de tinción con Coomassie (Figura 4). </li></ol> 3. PreScission escisión de la proteasa y Cromatografía de intercambio catiónico <ol><li> Añadir 50 unidades de proteasa PreScission al eluato MBP-Mgm101. Realizar la escisión en 4 ° CO / N y permitir que continúe durante la diálisis contra el tampón de diálisis (20 mM de Tris-HCl, pH 7,4, 100 mM de NaCl; DTT 2 mM, EDTA 1 mM, pH 7,4, y 0,2 mM PMSF) </li><li> Controlar la eficacia de la escisión en un gel de SDS-PAGE (Figura 5A). </li><li> Cargue el troceados MBP-Mgm101 por múltiples inyectariones en un cartucho Mini Macro-Prep High S Bio-Escala conectados a un sistema de FPLC de doble paso biológica Bio-Rad. </li><li> Iniciar la cromatografía de intercambio catiónico mediante la aplicación de un gradiente de paso de sal de 5 mM, 300 mM, 500 mM, 750 mM y 1,000 mM de NaCl que se crea mediante la mezcla de tampón A (5 mM de NaCl, 10 mM de fosfato de Na, pH 7,2; 1 mM PMSF) y Tampón B (NaCl 1 M, 10 mM de fosfato de Na, pH 7,2; 1 mM de PMSF). Establecer la velocidad de flujo a 0,5 ml / min. Recoger la fracción Mgm101 y comprobar la pureza de la proteína en un gel de SDS-PAGE (Figura 5B). </li></ol> 4. Cromatografía de Exclusión de Tamaño <ol><li> Combinar las fracciones de proteínas de cromatografía de intercambio catiónico. Dializar la proteína en el tampón de equilibrado GF (MOPS 20 mM, pH 7,0; NaCl 150 mM, EDTA 1 mM, pH 7,4; 5 mM 2-mercaptoetanol 0,2 mM PMSF). </li><li> Se concentra la proteína con columna de centrifugación de ultrafiltración Vivaspin 15R para reducir el volumen a ~ 1 ml por centrifugación a 3000 xg a 4 ° C. </li><li> Cargar Mgm101 ona calibrado Superose 6 prep columna grado equilibrada con el tampón de cromatografía (20 mM MOPS, pH 7,0, 150 mM NaCl, 5 mM de β-mercaptoetanol, 1 mM EDTA, pH 7,4; 0,2 mM PMSF). </li><li> Iniciar la exclusión por tamaño con el tampón de cromatografía se ejecute a una velocidad de flujo de 0,5 ml / min. </li><li> Reunir las fracciones de los purificados Mgm101 picos. Cargar alícuotas de las fracciones en un 12% SDS-PAGE para comprobar la calidad final de la proteína. </li><li> Concentrado de la proteína con Vivaspin 6, a continuación, congelar rápidamente las muestras en N2 líquido y se almacena a -80 ° C. </li><li> Usa los Mgm101 muestras dentro de 6-12 meses para el ensayo de unión al ADNmc (Figura 8) y para la visualización estructural por microscopía electrónica de transmisión (Figura 9). </li></ol>

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U.S.A. 96, 4279-4284 (1999).</li><li>Ploquin, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+and+structural+basis+for+a+bacteriophage+homolog+of+human+RAD52.">Functional and structural basis for a bacteriophage homolog of human RAD52.</a> Curr. Biol. 18, 1142-1146 (2008).</li><li>Chen, X. J., Guan, M. X., Clark-Walker, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MGM101,+a+nuclear+gene+involved+in+maintenance+of+the+mitochondrial+genome+in+Saccharomyces+cerevisiae.">MGM101, a nuclear gene involved in maintenance of the mitochondrial genome in Saccharomyces cerevisiae.</a> Nucl. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+properly+configured+ring+structure+is+critical+for+the+function+of+the+mitochondrial+DNA+recombination+protein.">A properly configured ring structure is critical for the function of the mitochondrial DNA recombination protein.</a> Mgm101. J. Biol. Chem. 287, 37259-37268 (2012).</li><li>Zuo, X., Xue, D., Li, N., Clark-Walker, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+functional+core+of+the+mitochondrial+genome+maintenance+protein+Mgm101p+in+Saccharomyces+cerevisiae+determined+with+a+temperature-conditional+allele.">A functional core of the mitochondrial genome maintenance protein Mgm101p in Saccharomyces cerevisiae determined with a temperature-conditional allele.</a> FEMS Yeast Res. 7, 131-140 (2007).</li><li>Itoh, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+packaging+proteins+Glom+and+Glom2+coordinately+organize+the+mitochondrial+nucleoid+of+Physarum+polycephalum.">DNA packaging proteins Glom and Glom2 coordinately organize the mitochondrial nucleoid of Physarum polycephalum.</a> Mitochondrion. 11, 575-586 (2011).</li><li>Janicka, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+RAD52-like+single-stranded+DNA+binding+protein+affects+mitochondrial+DNA+repair+by+recombination.">A RAD52-like single-stranded DNA binding protein affects mitochondrial DNA repair by recombination.</a> Plant J. 72, 423-435 (2012).</li></ol>

Los autores declaran que no tienen intereses financieros en competencia.

Ha sido un reto para producir una proteína estable, nativo recombinante Mgm101 de E. coli posiblemente debido a su insolubilidad en células bacterianas. En este informe, muestran que la estrategia de fusión MBP permite que la proteína que se expresa en un nivel razonablemente alto. Mediante el uso de tinción negativa microscopía electrónica de transmisión y cromatografía de exclusión por tamaño, hemos demostrado previamente que la proteína de fusión MBP forma oligómeros uniformes in vitro...

La recombinación homóloga es importante para la reparación de doble filamento se rompe (DSBs) y enlaces cruzados, y para la reiniciación de la replicación del ADN a partir de horquillas de replicación se derrumbó 1. En la recombinación homóloga convencional, el centro de reacción es catalizada por las recombinasas dependientes de ATP incluyendo RecA en procariotas, y Rad51 y Dmc1 en eucariotas 1-3. Estas recombinaciones forman nucleoprotein filamentos en ssDNA, que son esenciales para iniciar la búsqueda de homología y el capítulo invasión dentro de moldes de ADN dúplex (Figura 1, panel izquierdo) 4-7. Además del esquema convencional, la recombinación homóloga también puede tener lugar de una manera RecA/Rad51-independent (Figura 1, panel derecho). Por ejemplo, las proteínas de levadura Rad52 y Rad59 pueden catalizar directamente la hibridación de cadenas de ADNmc complementarias que están expuestos por resección de roturas de ADN de doble cadena. Este proceso de recombinación, conocido como cantarle línea de recocido, por lo general no implica homóloga de emparejamiento con las plantillas de ADN de doble cadena. Después del recocido, colas heterólogas se eliminan por exonucleasas y mellas se ligan para restaurar la continuidad del genoma 8-10. Reparación por el mismo mecanismo de recocido capítulo suele ir acompañada de las supresiones de secuencias genómicas entre las regiones directamente repetidas. Rad52 pertenece a un grupo diverso de proteínas de recombinación que son muy extendida entre bacteriófagos 11. Estas proteínas también se conocen como proteínas individuales de recocido Strand (SSAP), sobre la base de su actividad en la promoción de la hibridación de moléculas de ADN homólogas de cadena sencilla. Los mejores SSAP bacteriófagos son caracterizados Redβ y Erf del bacteriófagos λ y P22, RecT del profago rac y la proteína Sak del fago lactococcal UL36. Los SSAP se caracterizan estructuralmente por un típico pliegue β-β-β-α, aunque similitud es prácticamente indetectablepoder en sus secuencias primarias. Todos ellos forman grandes anillos homo-oligómeros de 10-14 simetría veces in vitro 12-14. Las consecuencias funcionales de la organización estructural de orden superior característica no se entiende bien. Estamos interesados ​​en la comprensión del mecanismo de la recombinación homóloga en el genoma mitocondrial. Anteriormente hemos identificado el gen MGM101 que es esencial para el mantenimiento de ADNmt en Saccharomyces cerevisiae 15. MGM101 posteriormente se encontró que se asocia con nucleoides mitocondriales y es necesario para la tolerancia de ADNmt a los agentes que dañan el ADN 16. Sin embargo, el estudio de Mgm101 ha sido muy limitado en la última década por la dificultad para producir Mgm101 recombinante. Hemos tenido éxito recientemente en la producción de Mgm101 soluble en grandes cantidades a partir de E. coli mediante la estrategia de fusión MBP. Esto nos ha permitido demostrar que Mgm101 accionessimilitudes bioquímicas y estructurales con la Rad52-familia de proteínas 17,18. En este informe, se describe un procedimiento de purificación de tres etapas, que produce los análisis bioquímicos y estructurales Mgm101for homogéneos (Figura 2).

<table border="1" fo:keep-together.within-page="always">
	<tbody>
		<tr>
			<td>Name of Reagent/Material</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Expression vector pMAL-c2E</td>
			<td>New England Biolabs</td>
			<td>#N8066S</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>PreScission Protease</td>
			<td>GE Healthcare Life Sciences</td>
			<td>#27-0843-01</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>BL21-CodonPlus(DE3)-RIL cells</td>
			<td>Strategene</td>
			<td>#230245</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Leupeptin</td>
			<td>Roche Applied Science</td>
			<td>#11034626001</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Pepstatin</td>
			<td>Roche Applied Science</td>
			<td>#11359053001</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Phenylmethylsulfonyl fluoride (PMSF)</td>
			<td>Roche Applied Science</td>
			<td>#10837091001</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>DNAse I</td>
			<td>Sigma</td>
			<td>#DN25-1G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Isopropyl &beta;-D-1-thiogalactopyranoside (IPTG)</td>
			<td>Roche Applied Science</td>
			<td>#11411446001</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Amylose resin</td>
			<td>New England Biolabs</td>
			<td>#E8021L</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Econo-Column chromatography column</td>
			<td>BIO-RAD</td>
			<td>#7372512</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bio-Scale Mini Macro-Prep High S cartridge (1 ml)</td>
			<td>BIO-RAD</td>
			<td>#732-4130</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>VIVASPIN 15R Ultrafiltration spin column (10,000 MWCO)</td>
			<td>Sartorius Stedium</td>
			<td>#VS15RH02</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Superose 6 prep grade column</td>
			<td>Amersham Bioscirnces</td>
			<td>#17-0489-01</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>VIVASPIN 6 Ultrafiltration spin column (5,000 MWCO)</td>
			<td>Sartorius Stedium</td>
			<td>#VS0611</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

preparation of the mgm101 recombination protein by mbp-based tagging strategy

El gen MGM101 se identificó hace 20 años por su papel en el mantenimiento de ADN mitocondrial. Los estudios de varios grupos han sugerido que la proteína Mgm101 está implicado en la reparación de recombinación de ADN mitocondrial. Recientes investigaciones han indicado que Mgm101 se relaciona con la familia de proteínas de recombinación de tipo Rad52. Estas proteínas forman grandes anillos de oligómeros y promueven la hibridación de moléculas de ADN homólogas de cadena sencilla. Sin embargo, la caracterización de Mgm101 se ha visto obstaculizada por la dificultad en la producción de la proteína recombinante. Aquí, se describe un procedimiento fiable para la preparación de Mgm101 recombinante. Proteína de unión a maltosa (MBP)-etiquetados Mgm101 se expresa primero en Escherichia coli. La proteína de fusión se purificó inicialmente por cromatografía de afinidad de amilosa. Después de ser liberado por escisión proteolítica, Mgm101 se separa de MBP por cromatografía de intercambio catiónico. Monodispersada Mgm101 se obtiene despuéspor cromatografía de exclusión por tamaño. Se obtiene un rendimiento de ~ 0,87 mg de Mgm101 por litro de cultivo bacteriano puede ser obtenido de forma rutinaria. El Mgm101 recombinante tiene un mínimo de contaminación de ADN. Las muestras preparadas se utilizan con éxito para el análisis de imágenes de partículas bioquímicas, estructurales e individuales de Mgm101. Este protocolo también se puede usar para la preparación de otras proteínas de unión al ADN oligoméricas grandes que pueden ser mal plegadas y tóxico para las células bacterianas.

Mgm101 es una proteína Rad52 recombinación relacionada en la mitocondria. Rad52 ha sido ampliamente estudiado por su papel en la recombinación del ADN mitocondrial (Figura 1). Mgm101 recombinante se puede preparar mediante un procedimiento de tres pasos (Figura 2). Esto se ve facilitado por el uso de la estrategia de MBP-etiquetado que permite Mgm101 a ser expresado en una forma soluble y posteriormente liberado de la etiqueta mediante escisión proteolítica (Figura 3).</str...

Watch this Scientific Journal Video about Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy at JoVE.com

Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy

La proteína nucleoide mitocondrial de levadura, Mgm101, es una proteína de recombinación de tipo Rad52 que forma grandes anillos de oligómeros. Un protocolo se describe la preparación Mgm101 recombinante soluble usando la proteína de unión a maltosa (MBP)-etiquetado estrategia junto con intercambio catiónico y cromatografía de exclusión por tamaño.

Preparación de la proteína de recombinación Mgm101 por Estrategia de etiquetas MBP basado

The MGM101 gene was identified 20 years ago for its role in the maintenance of mitochondrial DNA. Studies from several groups have suggested that the ...

preparation-mgm101-recombination-protein-mbp-based-tagging

Research

JoVE Journal

Biology

12.0K vistas.  State University of New York Upstate Medical University. La proteína nucleoide mitocondrial de levadura, Mgm101, es una proteína de recombinación de tipo Rad52 que forma grandes anillos de oligómeros. Un protocolo se describe la preparación Mgm101 recombinante soluble usando la proteína de unión a maltosa (MBP)-etiquetado estrategia junto con intercambio catiónico y cromatografía de exclusión por tamaño.

Video: Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy

Staining of Proteins in Gels with Coomassie G-250 without Organic Solvent and Acetic Acid

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents (Methanol, Ethanol or 2-Propanol) and acetic acid are used for fixation, staining and destaining of proteins in a gel after SDS-PAGE. To speed up the procedure, heating the staining solution in the microwave oven for a short time is frequently used. This usually results in evaporation of toxic or hazardous Methanol, Ethanol or 2-Propanol and a strong smell of acetic acid in the lab which should be avoided due to safety considerations. In a protocol originally published in two patent applications by E.M. Wondrak (US2001046709 (A1), US6319720 (B1)), an alternative composition of the staining solution is described in which no organic solvent or acid is used. The CBB is dissolved in bidistilled water (60-80mg of CBB G-250 per liter) and 35 mM HCl is added as the only other compound in the staining solution. The CBB staning of the gel is done after SDS-PAGE and thorough washing of the gel in bidistilled water. By heating the gel during the washing and staining steps, the process can be finished faster and no toxic or hazardous compunds are evaporating. The staining of proteins occurs already within 1 minute after heating the gel in staining solution and is fully developed after 15-30 min with a slightly blue background that is destained completely by prolonged washing of the stained gel in bidistilled water, without affecting the stained protein bands.

A short protocol for protein staining with Coomassie Brilliant Blue (CBB) G-250 in polyacrylamide gels is described without using organic solvents or acetic acid as in the classical staining procedures with CBB.

Tinción de las proteínas en geles con Coomassie G-250, sin ácido disolvente orgánico y el acético

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents ...

Investigación

Biología

Using the GELFREE 8100 Fractionation System for Molecular Weight-Based Fractionation with Liquid Phase Recovery

The GELFREE 8100 Fractionation System is a novel protein fractionation system designed to maximize protein recovery during molecular weight based fractionation. The system is comprised of single-use, 8-sample capacity cartridges and a benchtop GELFREE Fractionation Instrument. During separation, a constant voltage is applied between the anode and cathode reservoirs, and each protein mixture is electrophoretically driven from a loading chamber into a specially designed gel column gel. Proteins are concentrated into a tight band in a stacking gel, and separated based on their respective electrophoretic mobilities in a resolving gel. As proteins elute from the column, they are trapped and concentrated in liquid phase in the collection chamber, free of the gel. The instrument is then paused at specific time intervals, and fractions are collected using a pipette. This process is repeated until all desired fractions have been collected. If fewer than 8 samples are run on a cartridge, any unused chambers can be used in subsequent separations.
This novel technology facilitates the quick and simple separation of up to 8 complex protein mixtures simultaneously, and offers several advantages when compared to previously available fractionation methods. This system is capable of fractionating up to 1mg of total protein per channel, for a total of 8mg per cartridge. Intact proteins over a broad mass range are separated on the basis of molecular weight, retaining important physiochemical properties of the analyte. The liquid phase entrapment provides for high recovery while eliminating the need for band or spot cutting, making the fractionation process highly reproducible1.

The accompanying video describes the use of the GELFREE 8100 Fractionation System, which partitions complex protein samples on the basis of molecular weight and recovers the fractions in liquid phase. The video describes how the technology works, how it is used, and provides resultant data, with polyacrylamide gel electrophoresis analysis of fractionated bovine liver homogenate.

Utilizando el sistema de fraccionamiento GELFREE 8100 de peso molecular basado en Fraccionamiento con la recuperación de la fase líquida

The GELFREE 8100 Fractionation System is a novel protein fractionation system designed to maximize protein recovery during molecular weight based ...

Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1

The functional analysis of missense mutations can be complicated by the presence in the cell of the endogenous protein. Structure-function analyses of the BRCA1 have been complicated by the lack of a robust assay for the full length BRCA1 protein and the difficulties inherent in working with cell lines that express hypomorphic BRCA1 protein1,2,3,4,5. We developed a system whereby the endogenous BRCA1 protein in a cell was acutely depleted by RNAi targeting the 3'-UTR of the BRCA1 mRNA and replaced by co-transfecting a plasmid expressing a BRCA1 variant. One advantage of this procedure is that the acute silencing of BRCA1 and simultaneous replacement allow the cells to grow without secondary mutations or adaptations that might arise over time to compensate for the loss of BRCA1 function. This depletion and add-back procedure was done in a HeLa-derived cell line that was readily assayed for homologous recombination activity. The homologous recombination assay is based on a previously published method whereby a recombination substrate is integrated into the genome (Figure 1)6,7,8,9. This recombination substrate has the rare-cutting I-SceI restriction enzyme site inside an inactive GFP allele, and downstream is a second inactive GFP allele. Transfection of the plasmid that expresses I-SceI results in a double-stranded break, which may be repaired by homologous recombination, and if homologous recombination does repair the break it creates an active GFP allele that is readily scored by flow cytometry for GFP protein expression. Depletion of endogenous BRCA1 resulted in an 8-10-fold reduction in homologous recombination activity, and add-back of wild-type plasmid fully restored homologous recombination function. When specific point mutants of full length BRCA1 were expressed from co-transfected plasmids, the effect of the specific missense mutant could be scored. As an example, the expression of the BRCA1(M18T) protein, a variant of unknown clinical significance10, was expressed in these cells, it failed to restore BRCA1-dependent homologous recombination. By contrast, expression of another variant, also of unknown significance, BRCA1(I21V) fully restored BRCA1-dependent homologous recombination function. This strategy of testing the function of BRCA1 missense mutations has been applied to another biological system assaying for centrosome function (Kais et al, unpublished observations). Overall, this approach is suitable for the analysis of missense mutants in any gene that must be analyzed recessively.

We provide a method for testing BRCA1 variants in a tissue culture based assay for homologous recombination repair of DNA damage by depleting endogenous BRCA1 protein from a cell using RNAi and replacing it with a BRCA1 point mutant that contains a coding change.

La identificación de los efectos de las mutaciones BRCA1 en recombinación homóloga utilizando células que expresan endógeno de tipo salvaje BRCA1

The functional analysis of missense mutations can be complicated by the presence in the cell of the endogenous protein. Structure-function analyses of the ...

Genetic Modification and Recombination of Salivary Gland Organ Cultures

Branching morphogenesis occurs during the development of many organs, and the embryonic mouse submandibular gland (SMG) is a classical model for the study of branching morphogenesis. In the developing SMG, this process involves iterative steps of epithelial bud and duct formation, to ultimately give rise to a complex branched network of acini and ducts, which serve to produce and modify/transport the saliva, respectively, into the oral cavity1-3. The epithelial-associated basement membrane and aspects of the mesenchymal compartment, including the mesenchyme cells, growth factors and the extracellular matrix, produced by these cells, are critical to the branching mechanism, although how the cellular and molecular events are coordinated remains poorly understood 4. The study of the molecular mechanisms driving epithelial morphogenesis advances our understanding of developmental mechanisms and provides insight into possible regenerative medicine approaches. Such studies have been hampered due to the lack of effective methods for genetic manipulation of the salivary epithelium. Currently, adenoviral transduction represents the most effective method for targeting epithelial cells in adult glands in vivo5. However, in embryonic explants, dense mesenchyme and the basement membrane surrounding the epithelial cells impedes viral access to the epithelial cells. If the mesenchyme is removed, the epithelium can be transfected using adenoviruses, and epithelial rudiments can resume branching morphogenesis in the presence of Matrigel or laminin-1116,7. Mesenchyme-free epithelial rudiment growth also requires additional supplementation with soluble growth factors and does not fully recapitulate branching morphogenesis as it occurs in intact glands8. Here we describe a technique which facilitates adenoviral transduction of epithelial cells and culture of the transfected epithelium with associated mesenchyme. Following microdissection of the embryonic SMGs, removal of the mesenchyme, and viral infection of the epithelium with a GFP-containing adenovirus, we show that the epithelium spontaneously recombines with uninfected mesenchyme, recapitulating intact SMG glandular structure and branching morphogenesis. The genetically modified epithelial cell population can be easily monitored using standard fluorescence microscopy methods, if fluorescently-tagged adenoviral constructs are used. The tissue recombination method described here is currently the most effective and accessible method for transfection of epithelial cells with a wild-type or mutant vector within a complex 3D tissue construct that does not require generation of transgenic animals.

A technique to genetically manipulate epithelial cells within whole ex vivo cultured embryonic mouse submandibular glands (SMGs) using viral gene transfer is described. This method takes advantage of the innate ability of SMG epithelium and mesenchyme to spontaneously recombine after separation and infection of epithelial rudiments with adenoviral vectors.

Modificación genética y recombinación de las Glándulas Salivales culturas de órganos

Branching  morphogenesis occurs during the development of many organs, and the embryonic  mouse submandibular gland (SMG) is a classical model for the ...

Recombineering Homologous Recombination Constructs in Drosophila

The continued development of techniques for fast, large-scale manipulation of endogenous gene loci will broaden the use of Drosophila melanogaster as a genetic model organism for human-disease related research. Recent years have seen technical advancements like homologous recombination and recombineering. However, generating unequivocal null mutations or tagging endogenous proteins remains a substantial effort for most genes. Here, we describe and demonstrate techniques for using recombineering-based cloning methods to generate vectors that can be used to target and manipulate endogenous loci in vivo. Specifically, we have established a combination of three technologies: (1) BAC transgenesis/recombineering, (2) ends-out homologous recombination and (3) Gateway technology to provide a robust, efficient and flexible method for manipulating endogenous genomic loci. In this protocol, we provide step-by-step details about how to (1) design individual vectors, (2) how to clone large fragments of genomic DNA into the homologous recombination vector using gap repair, and (3) how to replace or tag genes of interest within these vectors using a second round of recombineering. Finally, we will also provide a protocol for how to mobilize these cassettes in vivo to generate a knockout, or a tagged gene via knock-in. These methods can easily be adopted for multiple targets in parallel and provide a means for manipulating the Drosophila genome in a timely and efficient manner.

Recombineering Homologous Recombination Constructs in Drosophila

Homologous recombination techniques greatly advance Drosophila genetics by enabling the creation of molecularly precise mutations. The recent adoption of recombineering allows one to manipulate large pieces of DNA and transform them into Drosophila6. The methods presented here combine these techniques to rapidly generate large homologous recombination vectors.

Recombinería homólogos Construcciones recombinación en<em&gt; Drosophila</em

The continued development of techniques for fast, large-scale manipulation of endogenous gene loci will broaden the use of Drosophila melanogaster as a ...

Improving the Success Rate of Protein Crystallization by Random Microseed Matrix Screening

Random microseed matrix screening (rMMS) is a protein crystallization technique in which seed crystals are added to random screens. By increasing the likelihood that crystals will grow in the metastable zone of a protein's phase diagram, extra crystallization leads are often obtained, the quality of crystals produced may be increased, and a good supply of crystals for data collection and soaking experiments is provided. Here we describe a general method for rMMS that may be applied to either sitting drop or hanging drop vapor diffusion experiments, established either by hand or using liquid handling robotics, in 96-well or 24-well tray format.

Here we describe a general method for random microseed matrix screening. This technique is shown to significantly increase the success rate of protein crystallization screening experiments, reduce the need for optimization, and provide a reliable supply of crystals for data collection and ligand-soaking experiments.

La mejora de la tasa de éxito de cristalización de proteínas por Random Matrix Microseed Screening

Random microseed matrix screening  (rMMS) is a protein crystallization technique in which seed crystals are added  to random screens. By increasing the ...

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli

The production of recombinant membrane proteins for structural and functional studies remains technically challenging due to low levels of expression and the inherent instability of many membrane proteins once solubilized in detergents. A protocol is described that combines ligation independent cloning of membrane proteins as GFP fusions with expression in Escherichia coli detected by GFP fluorescence. This enables the construction and expression screening of multiple membrane protein/variants to identify candidates suitable for further investment of time and effort. The GFP reporter is used in a primary screen of expression by visualizing GFP fluorescence following SDS polyacrylamide gel electrophoresis (SDS-PAGE). Membrane proteins that show both a high expression level with minimum degradation as indicated by the absence of free GFP, are selected for a secondary screen. These constructs are scaled and a total membrane fraction prepared and solubilized in four different detergents. Following ultracentrifugation to remove detergent-insoluble material, lysates are analyzed by fluorescence detection size exclusion chromatography (FSEC). Monitoring the size exclusion profile by GFP fluorescence provides information about the mono-dispersity and integrity of the membrane proteins in different detergents. Protein: detergent combinations that elute with a symmetrical peak with little or no free GFP and minimum aggregation are candidates for subsequent purification. Using the above methodology, the heterologous expression in E. coli of SED (shape, elongation, division, and sporulation) proteins from 47 different species of bacteria was analyzed. These proteins typically have ten transmembrane domains and are essential for cell division. The results show that the production of the SEDs orthologues in E. coli was highly variable with respect to the expression levels and integrity of the GFP fusion proteins. The experiment identified a subset for further investigation.

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli

A streamlined approach to screening for the expression of recombinant membrane proteins in Escherichia coli based on fusion to green fluorescent protein is presented.

Fluorescente verde a base de proteína Expresión Proyección de proteínas de membrana en<em&gt; Escherichia coli</em

The production of recombinant membrane proteins for structural and functional studies remains technically challenging due to low levels of expression and ...

Detecting Protein Subcellular Localization by Green Fluorescence Protein Tagging and 4',6-Diamidino-2-phenylindole Staining in Caenorhabditis elegans

In this protocol, a green fluorescence protein (GFP) fusion protein and 4',6-diamidino-2-phenylindole (DAPI) staining are used to track protein subcellular localization changes; in particular, a nuclear translocation under a heat stress condition. Proteins react correspondingly to external and internal signals. A common mechanism is to change its subcellular localization. This article describes a protocol to track protein localization that does not require an antibody, radioactive labeling, or a confocal microscope. In this article, GFP is used to tag the target protein EXL-1 in C. elegans, a member of the chloride intracellular channel proteins (CLICs) family, including mammalian CLIC4. An integrated translational exl-1::gfp transgenic line (with a promoter and a full gene sequence) was created by transformation and &#947;-radiation, and stably expresses the gene and gfp. Recent research showed that upon heat stress, not oxidative stress, EXL-1::GFP accumulates in the nucleus. Overlapping the GFP signal with both the nuclei structure and the DAPI signals confirms the EXL-1 subcellular localization changes under stress. This protocol presents two different fixation methods for DAPI staining: ethanol fixation and acetone fixation. The DAPI staining protocol presented in this article is fast and efficient and preserves both the GFP signal and the protein subcellular localization changes. This method only requires a fluorescence microscope with Nomarski, a FITC filter, and a DAPI filter. It is suitable for a small laboratory setting, undergraduate student research, high school student research, and biotechnology classrooms.

Detecting Protein Subcellular Localization by Green Fluorescence Protein Tagging and 4&#039;,6-Diamidino-2-phenylindole Staining in Caenorhabditis elegans

This protocol demonstrates how to track a protein nuclear translocation under heat stress by using a green fluorescence protein (GFP) fusion protein as a marker and 4',6-diamidino-2-phenylindole (DAPI) staining. The DAPI staining protocol is fast and preserves the GFP and protein subcellular localization signals.

Detección de localización subcelular de la proteína por etiquetado de proteína de fluorescencia verde y 4', 6-Diamidino-2-phenylindole coloración en Caenorhabditis elegans

In this protocol, a green fluorescence protein (GFP) fusion protein and 4',6-diamidino-2-phenylindole (DAPI) staining are used to track protein ...

Detecting and Characterizing Protein Self-Assembly In Vivo by Flow Cytometry

Protein self-assembly governs protein function and compartmentalizes cellular processes in space and time. Current methods to study it suffer from low-sensitivity, indirect read-outs, limited throughput, and/or population-level rather than single-cell resolution. We designed a flow cytometry-based single methodology that addresses all of these limitations: Distributed Amphifluoric FRET or DAmFRET. DAmFRET detects and quantifies protein self-assemblies by sensitized emission FRET in vivo, enables deployment across model systems-from yeast to human cells-and achieves sensitive, single-cell, high-throughput read-outs irrespective of protein localization or solubility.

This article describes a FRET-based flow cytometry protocol to quantify protein self-assembly in both S. cerevisiae and HEK293T cells.

Detección y caracterización de autoensamblaje de proteínas en Vivo por citometría de flujo

Protein self-assembly governs protein function and compartmentalizes cellular processes in space and time. Current methods to study it suffer from ...

An Improved Chemotaxis Assay for the Rapid Identification of Rhizobacterial Chemoattractants in Root Exudates

Chemotaxis identification is very important for the research and application of rhizosphere growth-promoting bacteria. We established a straightforward method to quickly identify the chemoattractants that could induce the chemotactic movement of rhizosphere growth-promoting bacteria on sterile glass slides via simple steps. Bacteria solution (OD600 = 0.5) and sterile chemoattractant aqueous solution were added dropwise on the glass slide at an interval of 1 cm. An inoculating loop was used to connect the chemoattractant aqueous solution to the bacterial solution. The slide was kept at room temperature for 20 min on the clean bench. Finally, the chemoattractant aqueous solution was collected for bacterial counting and microscopic observation. In this study, through multiple comparisons of experimental results, the method overcame multiple shortcomings of traditional bacterial chemotaxis methods. The method reduced the error of plate counting and shortened the experimental cycle. For the identification of chemoattractant substances, this new method can save 2-3 days compared to the traditional method. Additionally, this method allows any researcher to systematically complete a bacterial chemotaxis experiment within 1-2 days. The protocol can be considered a valuable resource for understanding plant-microbe interactions.

Here, we present an improved chemotaxis assay protocol. The goal of this protocol is to reduce the steps and costs of traditional bacterial chemotaxis methods and to serve as a valuable resource for understanding plant-microbe interactions.

Un ensayo de quimiotaxis mejorado para la identificación rápida de quimioatrayentes rizobacterianos en exudados radiculares

Chemotaxis identification is very important for the research and application of rhizosphere growth-promoting bacteria. We established a straightforward ...