FREQUENCY AND DIRECTIONALITY OF GENE CONVERSION EVENTS INVOLVING THE CYC7-H3 MUTATION IN SACCHAROMYCES CEREVISIAE

The CYC7-H3 mutation is a 5-kb deletion that causes overproduction of iso-2 cytochrome c. Unlike most mutations in yeast, the CYC7-H3 mutation is preferentially lost when it is involved in a gene conversion event. We have shown that cloned copies of CYC7-H3 DNA that are inserted into the yeast genome are associated with a high frequency of recombination and aberrant segregation events. Since parity in conversion frequency was observed when the extensive insertion/deletion heterozygosity at this locus was eliminated, we conclude that the CYC7-H3 sequences are inherently capable of acting as donors or recipients in gene conversion events, although they are unlikely to act as donors when they are located opposite a large heterology. DNA sequence comparisons revealed similarities between the CYC7-H3 junction region and the 2-µm circle DNA region that is involved in site-specific recombination.