During meiosis in wild-type cells,
homologous chromosomes become associated along their lengths by the
synaptonemal complex (SC). ZIP3 is a meiosis-specific gene of
Saccharomyces cerevisiae. To examine the effects of the
zip3 mutation on SC formation, meiotic chromosomes from
wild-type and zip3 cells were surface spread and stained with
antibodies to Zip1. Zip1 is a component of mature SC; thus, Zip1
localization to chromosomes serves as a marker for chromosome
synapsis. The zip3 mutant displays a substantial delay in SC
formation with Zip1 most often present in polycomplexes (aggregates of
SC proteins unassociated with chromatin). The zip3 mutant also
displays reductions in sporulation efficiency, meiotic recombination
and spore viability. The Zip3 protein localizes to discrete foci on
chromosomes during the period of SC formation. Zip3 foci colocalizes
with the Zip2 protein, which localizes to sites of synapsis initiation
and is required for SC formation. Zip3 also interacts with a number of
recombination proteins including proteins that act at both early
(Mre11 and Rad57) and late (Msh4 and Msh5) steps in meiotic
recombination. Our data suggest that Zip3 promotes synapsis by
recruiting and/or stabilizing the Zip2 protein on chromosomes. We
speculate that Zip3 is a component of recombination nodules and serves
to link meiotic recombination to the initiation of SC formation.
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