Abstract
Repairing a double-strand break by homologous recombination requires binding of the strand exchange protein Rad51p to ssDNA, followed by synapsis with a homologous donor. Here we used chromatin immunoprecipitation to monitor the in vivo association of
Saccharomyces cerevisiae Rad51p with both the cleaved MATa locus and the HMLα donor. Localization of Rad51p to
MAT precedes its association with HML, providing evidence of the time needed for the Rad51 filament to search the genome for a homologous sequence. Rad51p binding to ssDNA requires Rad52p. The absence of Rad55p delays Rad51p binding to ssDNA and prevents strand invasion and localization of Rad51p to HMLα. Lack of Rad54p does not significantly impair Rad51p recruitment to
MAT or its initial association with HMLα; however, Rad54p is required at or before the initiation of DNA synthesis after synapsis has occurred at the 3′ end of the invading strand.