Identification of factors that regulate the meiosis-specific recombinase DMC1

In Saccharomyces cerevisiae, the RecA homologs DMC1 and RAD51 are required for meiotic recombination. Genetic studies suggest that the functions of these two genes are partially redundant and that each plays a unique, although as yet unspecified, role during meiotic recombination. In order to study DMC1 function, a genetic screen for suppressor mutations was undertaken starting with a newly isolated temperature sensitive allele of the gene. Five complementation groups of recessive intergenic suppressors were identified. Four of the five groups do not suppress dmc1Delta meiotic arrest suggesting that the suppressors function by promoting Dmc1-dependent recombination, rather than bypassing the need for Dmc1 during meiotic recombination. All suppressed strains exhibit near wild type levels of spore viability and intragenic recombination levels at the HIS4 locus. Two approaches to identify the suppressors were carried out but were unsuccessful. All suppressors are recessive and likely represent loss of function alleles of the wild type genes, thus raising the possibility that negative regulation of Dmc1 occurs during wild type meiosis. Dmc1- and Rad51-mediated recombination is aided by accessory factors. TID1/RDH54 and RAD54, two members of the SWI2/SNF2 group of chromatin remodeling factors, act as accessory factors to the RecA homologues in vitro, though the exact mechanism through which they enhance recombination in vivo is unknown. Here, cytological and biochemical methods provide evidence that Dmc1 associates with chromatin in the absence of meiotic breaks and that Tid1 promotes dissociation of Dmc1 from DNA in an ATPase-dependent manner. tid1Delta mutants also exhibit meiotic arrest in the presence of reduced temperatures and in the presence of modest increases in Dmc1 levels. This novel finding suggests that at least one of Tid1's functions during meiosis involves regulating Dmc1-dependent activity, likely Dmc1's DNA binding activity. This activity may promote meiotic recombination in vivo.;The identification of a novel role for Tid1 and the identification of recessive mutations that promote Dmc1-dependent recombination provide evidence for the existence of recombination accessory factors that negatively regulate Dmc1-dependent recombination. How these findings contribute to understanding the regulation and function of Dmc1 function will be discussed.