Possible gene interchange between plasmid and chromosome in yeast

Genomic DNAs isolated from 420 yeast strains stocked in the Department of Fermentation Technology, Hiroshima university (HUT) were screened fro the presence of a plasmid sequence both as plasmid or in the chromosome. Five DNA samples gave rise to a positive hybridization signal wht 32 P‐labelled Zygosaccharomyces plasmid pSR1 was used as a probe. Two among these contain hybridzing sequences as plasmids while the other three apparently were chromosomal. Two chromosomal DNA segments of HUT 7195 ( Zygosaccharomyces spp .) which hybridized with pSR1 probe were cloned and sequenced. Both DNAs hybridized with a plasmid sequence covering the P gene of pSR1. One of hte tow segments contains a large open reading frame which can encode 410 amino acid residues. The deduced amino acid sequence is closely related with that of the P gene of pSR1. The present finding suggests that there was an interchange(s) of a gene between yeast plasmid(s) and chromosomes.