INITIATION OF RECOMBINATION IN SACCHAROMYCES-CEREVISIAE HAPLOID MEIOSIS

In most eukaryotes during prophase I of meiosis, homologous chromosome s pair and recombine by coordinated molecular and cellular processes, To directly test whether or not the early steps of the initiation of r ecombination depend on the presence of a homologous chromosome, we hav e examined the formation and processing of DNA double-strand breaks (D SBs, the earliest physical landmark of recombination initiation) in va rious haploid Saccharomyces cerevisiae strains capable of entering mei osis, We find that DSBs occur in haploid meiosis, showing that the pre sence of a homolog is not required for DSB formation, DSBs occur at th e same positions in haploid and diploid meioses, However, these two ty pes of meiosis exhibit subtle differences with respect to the timing o f formation and levels of DSBs, In haploid meiosis, a slower rate of D SB formation and a reduction in the frequency of DSB (at one of the th ree sites analyzed) were observed, These results might indicate that i nteractions between homologs play a role in the formation of meiotic D SBs, Furthermore, haploid strains exhibit a pronounced delay in the di sappearance of meiotic DSBs compared to diploid strains, which suggest s that sister chromatid interactions for DSB repair are inhibited in h aploid meiosis.