Partial Restoration of Sporulation Defect in Sake Yeasts, Kyokai No. 7 and No. 9,by Increased Dosage of the IME1 Gene

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Sake yeast (Saccharomyces cerevisiae) strains, Kyokai no. 7 and no. 9 sporulate little if at all. To determine the reason for their poor sporulation, we analyzed transcripts of the IME1 and IME2 (inducer of meiosis), and RMW1 (regulator of meiosis) genes. Kyokai no. 7 produced transcripts of IME1 and IME2 at low levels and their levels were not induced, but rather repressed, in sporulation conditions. Introduction of the cloned wild-type IME1 gene ligated to a multicopy plasmid into these cells partially restored their sporulation frequency in sporulation conditions. However, on dissection of asci no germination of spores was observed. A double transformant of Kyokai no. 7 with IME1 and IME2 plasmids did not show greater increase in sporulation frequency than a single transformant with the IME1 plasmid. The IME1 transcription level of the IME1 transformant cells of Kyokai no. 7 was the same as that of the wild-type wild-type a/α diploid cells, but the RME1 transcription level of these cells was severely repressed. Their level of IME2 transcription was much lower than that in the wild-type a/α diploid cells. An IME2-lacZ fusion gene, bearing a 1.1-kbp IME2 promoter region and ligated to a multicopy plasmid was not expressed in Kyokai no. 7 cells or in a/a cells. The IME2-lacZ fusion gene was, however, expressed in these cells by further introduction of a multicopy plasmid bearing the IME1 gene. Thus, we conclude that Kyokai no. 7 might have defects in the IME1 gene and its expression, and weakness in regulatory circuits for starvation signals and/or in the sporulation program.
1992-04-25

Partial Restoration of Sporulation Defect in Sake Yeasts, Kyokai No. 7 and No. 9,by Increased Dosage of the IME1 Gene

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