Mec1 Modulates Interhomolog Crossover and Interplays with Tel1 at Post Double-Strand Break Stages.

During meiosis I, programmed DNA double-strand breaks (DSBs) occur to promote chromosome pairing and recombination between homologs. In Saccharomyces cerevisiae , Mec1 and Tel1, the orthologs of human ATR and ATM, respectively, regulate events upstream of the cell cycle checkpoint to initiate DNA repair. Tel1 ^ATM and Mec1 ^ATR are required for phosphorylating various meiotic proteins during recombination. This study aimed to investigate the role of Tel1 ^ATM and Mec1 ^ATR in meiotic prophase via physical analysis of recombination. Tel1 ^ATM cooperated with Mec1 ^ATR to mediate DSB-to-single end invasion transition, but negatively regulated DSB formation. Furthermore, Mec1 ^ATR was required for the formation of interhomolog joint molecules from early prophase, thus establishing a recombination partner choice. Moreover, Mec1 ^ATR specifically promoted crossover-fated DSB repair. Together, these results suggest that Tel1 ^ATM and Mec1 ^ATR function redundantly or independently in all post-DSB stages.