We have shown previously
that pairing of homologous chromosomes occurs through multiple,
interstitial interactions along chromosome lengths in premeiotic yeast
(Weiner and Kleckner, 1994 Cell 77:977). We report here that homologous
chromosomes pair in vegetatively dividing diploid yeast. Fluorescence in
situ hybridization (FISH) and lox /cre site-specific recombination
were used to report on the relative frequency of interactions between
pairs of homologs and nonhomologs in spread nuclei and in living cells.
Both assays show that interactions between homologs occur more
frequently than interactions between nonhomologs. Moreover,
nonhomologous chromosomes interact in accordance with observations made
in many organisms that centromeres of all chromosomes cluster. We
analyzed the degree of homolog pairing throughout the vegetative cell
cycle by using the FISH assay. Homolog pairing is highest during G1 and
G2, lowest during S and reduced during M. Thus, homolog pairing in
vegetatively growing yeast is remarkably similar to meiotic homolog
pairing. Mutations in recombination /repair genes do not affect pairing
suggesting that an additional homology recognition system must exist to
pair homologs. Pairing occurs to the same extent in MATa/MATa and
MATa/MATalpha diploids and in several strain backgrounds. The
ability to isolate homolog pairing from meiotic events provides a
powerful starting point from which to identify and characterize the
factors involved. To this end, we have isolated pairing mutants using
the lox /Cre assay. Characteriztion of these mutants is
underway.
Return to YGM 1998 Abstract Index