Functions encoded by the yeast plasmid pSB3 isolated from Zygosaccharomyces rouxii IFO 1730 (formerly Saccharomyces bisporus var. mellis).

Functions encoded by the yeast plasmid pSB3 were analysed in Saccharomyces cerevisiae and Zygosaccharomyces rouxii. The autonomously replicating sequence (ARS) and partitioning mechanisms of pSB3 worked as satisfactorily in Z. rouxii ME3 as in the native host Z. rouxii IFO 1730 (formerly Saccharomyces bisporus var. mellis). The ARS in Z. rouxii ME3 was located within a 168 bp BanII-HindIII fragment spanning part of the inverted repeat (IR) and a unique region contiguous to it. The FLP enzyme (responsible for the intramolecular recombination at IRs) of pSB3 was functional in Z. rouxii ME3. In spite of the similarity of the putative recognition site for the FLP enzyme in pSB3 and pSR1, the FLP enzyme of pSB3 did not recognize the recombination site of pSR1, and the FLP enzyme of pSR1 did not use the recombination site of pSB3. Three transcripts of 3.4, 1.8 and 1.1 kb from pSB3 in Z. rouxii ME3 were identified by Northern blotting; they encompassed the A, B and C genes, respectively. pSB3 contained a region from which no poly(A)-containing RNA was transcribed.