REGULATION OF THE PROTEINASE-B STRUCTURAL GENE PRB1 IN SACCHAROMYCES-CEREVISIAE

The expression of PRB1, the gene that encodes the precursor to the sol uble vacuolar proteinase B (PrB) in Saccharomyces cerevisiae, is regul ated by carbon and nitrogen sources and by growth phase. Little or no PRB1 mRNA is detectable during exponential growth on glucose as the ca rbon source; it begins to accumulate as cells exhaust the glucose, Pre vious work has shown that glucose repression of PRB1 transcription is not mediated by HXK2 or by the SNF1, SNF4, and SNF6 genes (C. M. Moehl e and E. W. Jones, Genetics 124:39-55, 1990). We analyzed the effects of mutations in the MIG1, TUP1, and GRR1 genes on glucose repression o f PRB1 and found that mutations in each partially alleviate glucose re pression, tup1 and mig1 mutants fail to translocate all of the Prb1p i nto the lumen of the endoplasmic reticulum. A screen for new mutants r evealed mutations in MIG1 and REG1, genes already known to regulate gl ucose repression, as well as in three new genes that we have named PBD 1 to PBD3; all cause derepressed expression, Mutations that result in failure to completely derepress PRB1 were also identified in two new g enes, named PND1 and PND2. Good nitrogen sources, like ammonia, repres s PRB1 transcription; mutations in URE2 do not affect this response. D erepression upon transfer to a poor nitrogen source is dependent upon GLN3.