Homologous Recombination and DNA Double-strand Breaks

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1. On double-strand break repair model for recombination by lambda. (1) Proved double-strand gap repair. (2) Redalpha and redbeta are only lambda genes essential to this repair. (3) RecA, recBC, recD, recJ, recN, and ruvB gene functions of E. coli are not essential. (4) RecA protein might affect choice between crossover and non-crossover.2. We made a plasmid transfer system that allows recovery of both products of recombination and showed:(1) RecF pathway of E. coli is non-reciprocal. (2) A double-strand break stimulates recombination exaggerating this non-reciprocal nature. (3) These results support "successive half crossing-over model", which proposes that one event of recombination makes a DNA end that then stimulates a next event of recombination.3. We demonstrated the following in RecE pathway of E. coli: (1) A double strand break stimulates reciprocal double-strand gap repair. (2) Modification of a double strand end makes recombination non-reciprocal but does not alter its frequency. (3) These results led us to a model in which creation of a double-strand gap leads to one of the following three pathways: non-reciprocal recombination, reciprocal double-strand gap repair with crossing-over, and reciprocal double-strand gap repair without crossing-over.4. We analyzed mammalian homologous recombination especially gene targeting with BPV plasmid.