A genetic and physical analysis of the MAL1 and MAL3 standard strains of Saccharomyces cerevisiae

Naumov (1971, 1972, 1976) characterized two complementing functions required for maltose fermentation: MALp and MALg. The presence of either function alone is not sufficient to allow for the fermentation of maltose but diploids heterozygous for these loci were able to ferment. Using MALp, MALg and mal0 tester strains obtained from Naumov (a mal0 strain is a non-fermenting strain which does not complement either MALp or MALg strains), we have performed a genetic analysis on the maltose fermenting strains 4059 (MAL1) and 1412-4D (MAL3). These strains were shown to contain both the dominant MAL1 or MAL3 locus and an additional cryptic MALg. The presence of the dominant MAL1 or MAL3 locus alone is sufficient to enable the strain to ferment maltose and thus must contain both the MALp and MALg functions. The expression of the cryptic MALg in each strain must therefore be dependent upon the MALp function linked to the dominant locus. In 4059, the cryptic MALg locus is linked to the MAL3 locus and is thus denoted MAL3g. In 1412-4D, the cryptic MALg locus is linked to the MAL1 locus and is thus denoted MAL1g. Gel transfer analysis of these strains was able to detect genomic HindIII fragment linked to both the dominant MAL loci and the MALg loci using a probe derived from the MAL6 locus of the Saccharomyces strain CB11. The significance of this result with regard to the genome organization of the MAL loci is discussed.