Somatic pairing of homologs in budding yeast: existence and modulation

Abstract

FISH analysis of well-spread chromosomes reveals that homologs are paired in vegetatively growing budding yeast diploid cells, via multiple interstitial interactions, and independent of recA homologs and mating type heterozygosity. Pairing is present during G₁and G₂, and in cells arrested at G₁ by mating pheromone, but is disrupted during S phase. Thus, somatic pairing is qualitatively analogous to premeiotic and early meiotic pairing. S-phase pairing disruption occurs by a complex intranuclear program involving regional, nucleus-wide, and temporal determinants. Pairing is also disrupted in two G₂-arrest conditions (cdc13tsand nocodazole). Together these findings suggest that cell cycle signals may provoke pairing disruption by modulating underlying chromosome and/or chromatin structure. Whether the cell chooses to disrupt pairing contacts or not (e.g., S phase and G₂ arrest, but not G₁ arrest or normal G₁or G₂), could be dictated by functional considerations involving homolog/sister discrimination.

Keywords

• Homologs
• pairing
• cell cycle
• chromosomes
• yeast