Consequences of growth media, gene copy number, and regulatory mutations on the expression of the PRB1 gene of Saccharomyces cerevisiae.
Consequences of growth media, gene copy number, and regulatory mutations on the expression of the PRB1 gene of Saccharomyces cerevisiae.
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作者：
C. Moehle;E. W. Jones
葡萄糖在转录水平抑制PRB 1表达。然而，从葡萄糖阻遏释放最初不导致蛋白酶B（PrB）活性的积累，尽管转录去阻遏。PrB活性仅在细胞接近稳定期时在第二次转录去抑制时积累。在2 μ-基质粒上增加PRB 1基因剂量不能克服葡萄糖阻遏。葡萄糖介导的PRB 1抑制不受与SUC 2相同的遗传控制。突变的HXK 2基因，这赋予葡萄糖不敏感的表达分泌型转化酶，没有影响PRB 1的表达水平的PrB活性。在任何SNF 1-SNF 6基因突变的菌株不能derepress分泌型转化酶的合成，但在没有葡萄糖的情况下生长时derepress PrB的合成。SNF 2或SNF 5基因的突变导致PrB活性的积累达到野生型的十倍。观察到的抑制基因的多态性：在snf 5轴承株，该抑制基因的一个等位基因导致PrB水平升高，另一个等位基因导致野生型水平的PrB，没有等位基因抑制Suc-表型的snf 5突变体。重新检查已发表的数据SUC 2在snf 2和snf 5突变体的表达和检查PRB 1在这些突变体中的表达矛盾地表明，SNF 2和SNF 5基因产物可能作为基因表达的负调节因子。
Glucose represses PRB1 expression at the level of transcription. However, release from glucose repression initially does not result in accumulation of protease B (PrB) activity despite transcriptional derepression. PrB activity accumulates only upon a second transcriptional derepression as the cells approach stationary phase. Increasing the PRB1 gene dosage on 2 mu-based plasmids does not overcome glucose repression. Glucose-mediated repression of PRB1 is not subject to the same genetic controls as SUC2. Mutation of the HXK2 gene, which confers glucose-insensitive expression of secreted invertase, had no effect on PRB1 expression at the level of PrB activity. Strains bearing a mutation in any of the SNF1-SNF6 genes cannot derepress secreted invertase synthesis, but did derepress PrB synthesis when grown in the absence of glucose. Mutation of the SNF2 or SNF5 gene led to accumulation of PrB activity to levels ten times that of wild type. Polymorphism for a suppressor gene was observed: in snf5-bearing strains, one allele of this suppressor gene resulted in elevated levels of PrB and the other allele resulted in wild-type levels of PrB; neither allele suppressed the Suc- phenotype of the snf5 mutant. Re-examination of published data on SUC2 expression in snf2 and snf5 mutants and examination of PRB1 expression in these mutants paradoxically suggest that the SNF2 and SNF5 gene products might act as negative regulators of gene expression.