Abstract
Diploid
Saccharomyces
cells experiencing a double-strand break (DSB) on one homologous chromosome repair the break by
RAD51
-mediated gene conversion >98% of the time. However, when extensive homologous sequences are restricted to one side of the DSB, repair can occur by both
RAD51
-dependent and
RAD51
-independent break-induced replication (BIR) mechanisms. Here we characterize the kinetics and checkpoint dependence of
RAD51
-dependent BIR when the DSB is created within a chromosome. Gene conversion products appear within 2 h, and there is little, if any, induction of the DNA damage checkpoint; however,
RAD51
-dependent BIR occurs with a further delay of 2 to 4 h and cells arrest in response to the G
2
/M DNA damage checkpoint.
RAD51
-dependent BIR does not require special facilitating sequences that are required for a less efficient
RAD51
-independent process.
RAD51
-dependent BIR occurs efficiently in G
2
-arrested cells. Once repair is initiated, the rate of repair replication during BIR is comparable to that of normal DNA replication, as copying of >100 kb is completed less than 30 min after repair DNA synthesis is detected close to the DSB.