engleski

RecA730 suppresses UV sensitive phenotype in recA loading mutants of Escherichia coli

Homologous recombination is a process important in the repair of double strand breaks (DSB), single strand gaps (SSG) and collapsed replication forks. The central part of the recombination process is binding of RecA protein to ssDNA, i. e., production of RecA filament. Depending on the type of lesion, there are two pathways that operate in Escherichia coli: RecBCD and RecF. In wild-type (wt) Escherichia coli strains, DSBs are processed by the RecBCD pathway, where the same enzyme performs and coordinates all activities necessary for RecA filament formation: helicase, nuclease and RecA loading. SSGs utilize the RecF recombination pathway where the functions are provided by different proteins (RecQ helicase, RecJ nuclease and RecFOR complex which provides RecA loading activity) [1]. These pathways are interchangeable in a recB1080 mutant which is nuclease and RecA loading deficient [2]. We have studied a specific recA mutant named recA730 (RecAE38K) which encodes a form of RecA protein that is able to achieve binding to ssDNA without the help of RecFOR loading mediators [3]. We tested weather recA730 mutation can suppress UV deficient phenotype of recB1080 mutants and its derivates. The results show that the recA730 mutation suppresses DNA repair deficiency in cells where both mechanisms for RecA filament formation are inactivated by mutations in genes for mediator proteins involved in RecA loading. In contrast, the suppression of DNA repair and recombination is not possible in cells where the defect is at the level of nuclease activity [4]. [1] Kowalczykowski S.C., (2000) Initiation of genetic recombination and recombination-dependent replication. Trends Biochem. Sci. 25, 156-165. [2] Ivančić-Baće, I., Peharec, P., Moslavac, S., et al. (2003) RecFOR function is required for DNA repair and recombination in a RecA loading-deficient recB mutant of Escherichia coli. Genetics 163, 485-494. [3] Wang, T.C.V., Chang, H.Y., Hung, J.L. (1993) Cosuppression of recF, recR and recO mutations by mutant recA alleles in Escherichia coli cells. Mutat. Res. 294, 157-166. [4] Vlašić, I. et al. (2011) The recA730 dependent suppression of recombination deficiency in RecA loading mutants of Escherichia coli. Res. Microbiol. 162: 262-269.

RecA loading; RecA730; UV sensitivity

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