The roles of Tel1, Srs2 and Rad6 during meiotic DSB repair.

Meiosis is a cell division in which one diploid parent cell produces four haploid daughter cells. Accurate alignment and segregation of homologous chromosomes during metaphase is critical for a successful meiotic division and viable gametes. Three concomitant events are required for a successful meiotic division: chromosome pairing, synapsis and recombination. Recombination is initiated by programmed induction of DNA double-strand breaks (DSBs). Interchromosomal repair of meiotic DSBs can form a crossover leading to genetic diversity by modifying linkage groups. Crossovers also tether the homologous chromosomes and help resist the tension of the first meiotic spindle. Controlled recombination is required for a successful meiotic division and segregation, however, recombination has to be tightly regulated. This work investigates the roles of Te11,Rad6 and Srs2 during meiotic homologous DSB repair. Tel1 is protein kinase required for initiating a signalling cascade in response to many forms of DNA damage. Tel1 has also been proven to function during meiosis and has been shown in some conditions to initiate a signalling cascade after the initiation of meiotic DSBs. In this work Tel1 is shown to influence the early stages of DSB repair during meiosis, however this is not in response to the formation of Spo11-DSB. Recombination ensures genetic variation and correct homologue alignment during meiosis I therefore is extremely important and tightly controlled. Srs2 is known to be a negative regulator of recombination and is important for normal sporeulation and viability in yeast. Analysis of an experimental site specific DSB (made by VDE) and at natural Spo11-DSBs indicates that in the absence of Srs2 the rate of repair can be increased at Spo11-DSBs and decreased at the VDE-DSB. One potential role for Srs2 during meiosis is to dismantle recombination intermediates formed between the sister chromatids. Rad6 is required for wild type amounts of Spo11-DSB formation. This work investigated the VDE-DSB repair in the absence of Rad6, and discovered that Rad6 has a role in the initiation of repair. Rad6 ubiquitinates histone H2B, and further analyses suggest that this modification is required for repair at the VDEDSB. Each of the genes studied is required for wild type repair of VDE-DSBs and Spo11-DSBS, even though they come from widely different functional groups. This illustrates the diversity of cellular pathways controlling the initiation and regulation of meiotic recombination