THE MEIOSIS-SPECIFIC HOP2 PROTEIN OF SACCHAROMYCES-CEREVISIAE ENSURESSYNAPSIS BETWEEN HOMOLOGOUS CHROMOSOMES

The hop2 mutant of S. cerevisiae displays a novel phenotype: meiotic c hromosomes form nearly wild-type amounts of synaptonemal complex, but most chromosomes are engaged in synapsis with nonhomologous partners. The meiosis-specific Hop2 protein localizes to chromosomes prior to an d during synapsis and in the absence of the double-strand breaks that initiate recombination. hop2 strains sustain a wild-type level of meio tic double-strand breaks, but these breaks remain unrepaired. The hop2 mutant arrests at the pachytene stage of meiotic prophase with the Re cA-like protein Dmc1 located at numerous sites along synapsed chromoso mes. We propose that the Hop2 protein functions to prevent synapsis be tween nonhomologous chromosomes.