2 YEAST CHROMOSOMES ARE RELATED BY A FOSS IL DUPLICATION OF THEIR CENTROMERIC REGIONS

A 15 kbp fragment of the Saccharomyces cerevisiae genome was cloned an d localised to the centromeric region of chromosome XIV by genetic lin kage and DNA sequencing. It bad a strong sequence similarity and a con served gene linkage and transcriptional orientation relatively to the centromeric region of chromosome III, indicating a fossil interchromos omal duplication of several linked genes. On chromosome XIV, the dupli cated fragment included the centromere, four genes (FUN34, CIT1 and tw o tDNAs), one open reading frame (DOM34) and a truncated delta element . Additional inserts bearing unique genes were present on the centrome ric region of chromosome III. The level of silent substitutions indica ted a relatively ancient genetic separation, pre-dating the emergence of S. cerevisiae and S. douglasii as distinct species. The ensuing evo lution of the duplicated regions retained strict sequence identity for the two tDNAs pairs, but was partially divergent for CIT1 and FUN34, and generated a probable pseudogenic equivalent of DOM34 on chromosome III. Extant multigenic duplications of this type might play an import ant role in the evolution of eukaryotic genomes.