TELOMERE-MEDIATED CHROMOSOME-PAIRING DURING MEIOSIS IN BUDDING YEAST

Certain haploid strains of Saccharomyces cerevisiae can undergo meiosi s, but meiotic prophase progression and subsequent nuclear division ar e delayed if these haploids carry an extra chromosome (i.e., are disom ic). Observations indicate that interactions between homologous chromo somes cause a delay in meiotic prophase, perhaps to allow time for int erhomolog interactions to be completed. Analysis of meiotic mutants de monstrates that the relevant aspect of homolog recognition is independ ent of meiotic recombination and synaptonemal complex formation. A dis ome in which the extra chromosome is circular sporulates without a del ay, indicating that telomeres are important for homolog recognition. C onsistent with this hypothesis, fluorescent in situ hybridization demo nstrates that a circular chromosome has a reduced capacity to pair wit h its homolog, and a telomere-associated meiotic protein (Ndj1) is req uired to delay sporulation in disomes. A circular dimer containing two copies of the same chromosome delays meiosis to the same extent as tw o linear homologs, implying that physical proximity bypasses the requi rement for telomeres in homolog pairing. Analysis of a disome carrying two linear permuted chromosomes suggests that even nonhomologous chro mosome ends can promote homolog pairing to a limited extent. We specul ate that telomere-mediated chromosome movement and/or telomere cluster ing promote homolog pairing.