Regulation of the GAL structural genes in the yeast Saccharomyces cerevisiae is implemented by the products of GAL-specific (GAL4, GAL80, GAL3) and general (GAL11, SWI1, 2, 3, SNF5, 6, numerous glucose repression) genes. Recent work has 1) yielded significant new insights on the DNA binding and transcription activation/Gal80 protein binding functions of the Gal4 activator protein, 2) described the characterization of purified Gal4 protein-Gal80 protein complexes, 3) deconvoluted the multiple and complex glucose repression pathways acting on GAL genes, 4) suggested a new mechanism for the Gal3 protein-mediated induction of GAL structural gene expression, 5) introduced Gal1 protein, a structural gene product, into the regulation scheme, and 6) extended our already substantial understanding of GAL regulatory gene control. The mechanisms which control structural and regulatory gene expression in the GAL family are compared and GAL structural/regulatory gene chromatin structure is discussed.

Amphotericin B potentiates the antifungal effects of 5-fluorocytosine and rifampicin, probably by increasing the penetration of these agents through the fungal cytoplasmic membrane.

The srbl-1 mutation of Saccharomyces cerevisiae is an ochre allele which renders the yeast dependent on an osmotic stabilizer for growth and gives the cells the ability to lyse on transfer to hypotonic conditions. A DNA fragment which complements both of these phenotypic effects has been cloned. This clone contains a functional gene which is transcribed into a 2.3-kb polyadenylated mRNA molecule. Transformation of yeast strains carrying defined suppressible alleles demonstrated that the cloned fragment does not contain a nonsense suppressor. Integrative transformation and gene disruption experiments, when combined with classical genetic analysis, confirmed that the cloned fragment contained the wild-type SRB1 gene. The integrated marker was used to map SRB1 to chromosome XV by Southern hybridization and pulsed-field gel electrophoresis. A disruption mutant created by the insertion of a TRP1 marker into SRBI displayed only the lysis ability phenotype and was not dependent on an osmotic stabilizer for growth. Lysis ability was acquired by growth in (or transfer to) an osmotically stabilized environment, but only under conditions which permitted budding. It is inferred that budding cells lyse with a higher probability and that weak points in the wall at the site of budding are involved in the process. The biotechnological potential of the cloned gene and the disruption mutant is discussed. (15), and elevated levels of protein excretion (31). The srbl-J mutation (previous designation, srbl; 15) has been found to produce defects in both the cell wall and the membrane. The walls of mutant cells contain less mannan than do those of the parent, and this mannan has an increased proportion of short side chains (17). The glucan structure of the walls of srbl-l mutants has also been found to be altered, being less branched in nature than that of the walls of the wild type (2a). The pleiotropic effects of the mutation are not confined to the wall, however, since alterations in the lipid composition of the plasma membrane have also been observed (22b).It is not clear which of these effects is a direct consequence of the mutation and which is secondary in nature. Nevertheless, the range of effects suggests that the wild-type SRB1 gene encodes a protein which plays a major role in determining the structural integrity of the yeast cell. This, together with the practical utility of the mutant in the laboratory and its potential for the commercial production of yeast extracts (26,30), means that it is important to characterize the SRBI gene and identify its product. In this paper, we report the cloning and characterization of SRBI, as well as the construction by gene disruption of mutations which shed further light on its physiological role. MATERIALS AND METHODSStrains and media. The S. cerevisiae and Escherichia coli strains used in this study are listed in Table 1.The media used for the growth of yeast cells (YEPD, presporulation, sporulation, and selective dropout minimal media with appropriate combinations of amino acids or ...

No abstract