A Saccharomyces servazzii clone homologous to Saccharomyces cerevisiae chromosome III spanning KAR4, ARS 304 and SPB1 lacks the recombination enhancer but contains an unknown ORF.

In order to learn about the evolutionary conservation of the recombination enhancer (RE) that controls donor preference during mating type switching in Saccharomyces cerevisiae, we have cloned a 13 kb region from S. servazzii. We find that the order of four genes surrounding the RE in S. cerevisiae (PRD1, KAR4, SPB1 and PBN1) is preserved in S.servazzii. However, there is an additional ORF in S. servazzii between PRD1 and KAR4 that is not homologous to any gene in S. cerevisiae or to genes in other organisms. Despite a 75-79% amino acid identity for KAR4 and SPB1, respectively, the S. servazzii sequence did not carry a well-conserved RE sequence and these sequences lacked RE function when introduced into S. cerevisiae. The S. servazzii region contains a sequence that supports autonomous DNA replication in S. cerevisiae and may represent a homologue of ARS304. The S. servazziii sequence has Genbank Accession No. BankIt359091 AF307954.