Telomere-led bouquet formation facilitates homologous chromosome pairing and restricts ectopic interaction in fission yeast meiosis.

A polarized chromosomal arrangement with clustered telomeres in a meiotic prophase nucleus is often called bouquet and is thought to be important for the pairing of homologous chromosomes. Fluorescence in situ hybridization in fission yeast indicated that chromosomal loci are positioned in an ordered manner as anticipated from the bouquet arrangement. Blocking the formation of the telomere cluster with the kms1 mutation created a disorganized chromosomal arrangement, not only for the regions proximal to the telomere but also for interstitial regions. The kms1 mutation also affected the positioning of a linear minichromosome. Consistent with this cytological observation, the frequency of ectopic homologous recombination between a linear minichromosome and a normal chromosome increased in the kms1 background. Intragenic recombination between allelic loci is reduced in the kms1 mutant, but those between non-allelic loci are unaffected or slightly increased. Thus, telomere-led chromosome organization facilitates homologous pairing and also restricts irregular chromosome pairing during meiosis.