engleski

The RuvABC resolvase is indispensable for recombinational repair in sbcB15 mutants of Escherichia coli

The RuvABC proteins of Escherichia coli play an important role in the processing of Holliday junctions during homologous recombination and recombinational repair. Mutations in the ruv genes have a moderate effect on recombination and repair in wild type strains but confer pronounced recombination deficiency and extreme sensitivity to DNA-damaging agents in a recBC sbcBC background. Genetic analysis presented in this work has revealed that the delruvABC mutation causes an identical DNA repair defect in UV- irradiated recBC sbcBC, sbcBC, and sbcB strains, indicating that the sbcB mutation alone is responsible for the extreme UV sensitivity of recBC sbcBC ruv derivatives. In experiments with gamma irradiation and in conjugational crosses, however, sbcBC delruvABC and sbcB delruvABC mutants displayed higher recombination proficiency than the recBC sbcBC delruvABC strain. The frequency of conjugational recombination observed with the sbcB delruvABC strain was quite similar to that of the delruvABC single mutant, indicating that the sbcB mutation does not increase the requirement for RuvABC in a recombinational process starting from pre-existing DNA ends. The difference between results obtained in three experimental systems used suggests that in UV- irradiated cells, the RuvABC complex might act in an early stage of recombinational repair. The results of this work are discussed in the context of recent recombination models which propose the participation of RuvABC proteins in the processing of Holliday junctions made from stalled replication forks. We suggest that the mutant SbcB protein stabilizes these junctions and makes their processing highly dependent on RuvABC resolvase.

Escherichia coli ; Homologous recombination ; RuvABC resolvase ; Holliday junctions

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