Biomedical subjects

M M Cox

Publications and source records attributed to M M Cox.

112 records · Page 7Linked to original sources

PubMed1981

A simple and rapid procedure for the large scale purification of the recA protein of Escherichia coli.

A simple and rapid three-step procedure for the large scale purification of the recA protein of Escherichia coli is described. The method depends primarily on a single chromatographic step which is highly specific for recA protein: elution by ATP from single-stranded DNA cellulose. With this procedure, gram quantities of recA protein, greater than 99% pure, can be reproducibility prepared for biochemical and biophysical analysis.

Ammonium Sulfate↗

PubMed1981

Renaturation of DNA: a novel reaction of histones.

Histones isolated from several sources, either singly or in combination promote the renaturation of complementary single strands of DNA, as measured by the acquisition of resistance to S1 nuclease. The reaction is rapid (T1/2 less than 1 min), and is stoichiometric rather than catalytic. Renaturation is stimulated by Mg2+, Mn2+, and Ca2+, but is strongly inhibited by Zn2+. Crude extracts of early embryos of Drosophila melanogaster possess renaturation activity which is protease sensitive, heat-stable, and acid-soluble, suggesting that most or all of it can be attributed to histones. This observation thus provides a functional assay for histones that should prove useful in studies of chromatin and histone-DNA interactions, as well as for the identification and isolation of histones and histone-like proteins in crude extracts.

Animals↗

PubMed1981

Directionality and polarity in recA protein-promoted branch migration.

The recA protein of Escherichia coli promotes the complete exchange of strands between full-length linear duplex and single-stranded circular phi X174 DNA molecules. Analysis of the reaction by electron microscopy confirms that D loops containing short heteroduplex regions are rapidly formed at the ends of the linear duplex, followed by a relatively slow branch migration that converts the D loops to nicked circular duplexes (RFII) and displaced linear single strands. Heteroduplex extension and displacement of the linear single strand are concerted. Heterologous sequences within the linear duplex halt branch migration and lead to the accumulation of D loops. Although D loops can be formed at either end of the linear duplex, recA protein-promoted branch migration proceeds uniquely in the 3' leads to 5' direction relative to the (--) strand of the linear duplex.

Bacterial Proteins↗

PubMed1981

recA protein of Escherichia coli promotes branch migration, a kinetically distinct phase of DNA strand exchange.

The recA protein of Escherichia coli promotes the complete exchange of strands between full-length linear duplex and single-stranded circular DNA molecules of bacteriophage phi X-174, converting more than 50% of the single-stranded DNA into heteroduplex replicative form II-like structures. Kinetically, the reaction can be divided into two phases, formation of short heteroduplex regions (D loops) and extension of the D loops via branch migration. recA protein participates directly in both phases. D loops are formed efficiently in the presence of ATP or the nonhydrolyzable ATP analog adenosine 5'-[gamma-thio]triphosphate, whereas D-loop extension requires continuous ATP hydrolysis. Complete strand exchange requires a stoichiometric amount of recA protein and is strongly stimulated by the single-stranded-DNA-binding protein of E. coli.

Bacterial Proteins↗