M. Castillo Cozar,1
Peter L. Graumann,2,
and
Juan C. Alonso1*
Department Microbial Biotechnology, Centro Nacional de Biotecnología, CSIC, C/Darwin 3, Campus Universidad Autónoma de Madrid, 28049 Madrid, Spain,1 Biochemie, Fachbereich Chemie, Hans-Meerwein-Straße, Philipps-Universität Marburg, 35032 Marburg, Germany2
Received 13 June 2005/ Accepted 19 October 2005
The recognition and processing of double-strand breaks (DSBs) to a 3' single-stranded DNA (ssDNA) overhang structure in Bacillus subtilis is poorly understood. Mutations in addA and addB or null mutations in recJ (
recJ), recQ (
recQ), or recS (
recS) genes, when present in otherwise-Rec+ cells, render cells moderately sensitive to the killing action of different DNA-damaging agents. Inactivation of a RecQ-like helicase (
recQ or
recS) in addAB cells showed an additive effect; however, when
recJ was combined with addAB, a strong synergistic effect was observed with a survival rate similar to that of
recA cells. RecF was nonepistatic with RecJ or AddAB. After induction of DSBs, RecN-yellow fluorescent protein (YFP) foci were formed in addAB
recJ cells. AddAB and RecJ were required for the formation of a single RecN focus, because in their absence multiple RecN-YFP foci accumulated within the cells. Green fluorescent protein-RecA failed to form filamentous structures (termed threads) in addAB
recJ cells. We propose that RecN is one of the first recombination proteins detected as a discrete focus in live cells in response to DSBs and that either AddAB or RecQ(S)-RecJ are required for the generation of a duplex with a 3'-ssDNA tail needed for filament formation of RecA.
Present address: Institut für Mikrobiologie, Universität Freiburg, Verfügungsgebäude, Stefan-Meier-Str. 17, 79104 Freiburg, Germany.
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