Results from Tomomi Tsubouchi and Shirleen Roeder (Yale University, New Haven, CT) suggest that centromeres might bring meiotic chromosomes together for a round of speed dating to find their ultimate partner.
Meiotic homologue pairing involves an interplay between genetic recombination and the formation of the synaptonemal complex (SC), which bridges homologous chromosomes. The new results show that one SC protein, Zip1, also bridges nonhomologues at early stages of prophase I in budding yeast.
Zip1 was seen at centromeres in foci, with the number of foci matching the number of chromosome pairs in the cell. The pairs did not need to be homologues—even in haploid cells, which lack homologues, chromosomes paired at their centromeres.
The number of centromeric Zip1 foci remained constant throughout prophase even as the number of homologous pairs increased, suggesting that partners are exchanged until the right pairing is achieved. “Zip1 may hold centromeres together long enough for chromosomal homology to be assessed,” suggests Roeder. The onset of recombination might then signal Zip1 extension, which was seen proceeding from centromeric regions in later stages of prophase.
The loss of Zip1 is known not to impair homologue pairing. But Roeder hypothesizes that it may become more important when other mechanisms that contribute to pairing are impaired.