Radcliffe P, Trevethick J, Tyers M, Sudbery P
Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, U.K.
Yeast. 1997 Jun 30;13(8):707-15. doi: 10.1002/(SICI)1097-0061(19970630)13:8<707::AID-YEA130>3.0.CO;2-9.
Wild-type cells of the budding yeast Saccharbmyces cerevisiae arrest in G1 upon nutrient exhaustion. Cell cycle arrest requires the WHI2 gene since whi2 mutants continue to divide and become abnormally small as nutrients are depleted. Here we show that CLN1 and CLN2 transcript levels in a whi2 strain are higher during exponential growth, and persist longer upon starvation, than in an isogenic wild-type strain. In contrast to CLN1 and CLN2, CLN3 levels declined only at very high cell density and were unaffected by the whi2 mutation. Elevated CLN expression is sufficient to explain the whi2 phenotype since ectopic expression of CLN1 in a nutrient-depleted culture caused cells to continue dividing and interfered with the acquisition of heat resistance. These observations show that, either directly or indirectly, Whi2 negatively regulates G1 cyclin expression. Interestingly extremely high levels of Cln1 induced filamentous growth upon nutrient deprivation, suggesting a direct connection between G1 cyclin activity and morphological responses to poor nutrient conditions.
出芽酵母酿酒酵母的野生型细胞在营养耗尽时会停滞在G1期。细胞周期停滞需要WHI2基因，因为当营养物质耗尽时，whi2突变体继续分裂并变得异常小。我们在此表明，与同基因野生型菌株相比，whi2菌株中CLN1和CLN2的转录水平在指数生长期更高，并且在饥饿时持续时间更长。与CLN1和CLN2不同，CLN3水平仅在非常高的细胞密度时下降，并且不受whi2突变的影响。CLN表达升高足以解释whi2表型，因为在营养耗尽的培养物中CLN1的异位表达导致细胞继续分裂并干扰耐热性的获得。这些观察结果表明，Whi2直接或间接地负调控G1期细胞周期蛋白的表达。有趣的是，在营养剥夺时，极高水平的Cln1诱导丝状生长，这表明G1期细胞周期蛋白活性与对不良营养条件的形态反应之间存在直接联系。
