Bose Sohini, Dutko James A, Zitomer Richard S
Department of Biological Sciences, University at Albany/SUNY, New York 12222, USA.
Genetics. 2005 Mar;169(3):1215-26. doi: 10.1534/genetics.104.034603. Epub 2004 Nov 15.
The general stress response of yeast involves the induction of approximately 200 genes in response to any one of several stresses. These genes are activated by Msn2 and repressed by the Srb10 kinase, a member of the mediator complex. Normally, Msn2 is exported from the nucleus, and Srb10 represses STRE gene expression. Under stress, Msn2 relocalizes to the nucleus and, with the relief of Srb10 repression, activates transcription. The stress response is rapid, but quickly attenuated. We show here that this attenuation is due to a nuclear-dependent degradation of Msn2. Msn2 rapidly disappeared from cells after heat or osmotic shock. This disappearance was not due to a change in MSN2 RNA levels, which remain constant during stress. Pulse-chase experiments confirmed the stress-dependent Msn2 degradation. The levels of Msn2 were significantly reduced in msn5 deletion cells that have been shown to constitutively retain Msn2 in the nucleus. The degradation was Srb10-dependent; Msn2 was not degraded in an srb10 deletion mutant. An Msn2 internal deletion mutant was insensitive to Srb10 repression, but was degraded by the Srb10-dependent mechanism. Thus, this mutation uncoupled Srb10 repression from degradation.
酵母的一般应激反应涉及在应对多种应激中的任何一种时诱导约200个基因。这些基因由Msn2激活，并被中介体复合物的成员Srb10激酶抑制。正常情况下，Msn2从细胞核输出，Srb10抑制STRE基因表达。在应激状态下，Msn2重新定位于细胞核，随着Srb10抑制作用的解除，激活转录。应激反应迅速，但很快减弱。我们在此表明，这种减弱是由于Msn2的核依赖性降解。热休克或渗透休克后，Msn2迅速从细胞中消失。这种消失不是由于MSN2 RNA水平的变化，其在应激期间保持恒定。脉冲追踪实验证实了应激依赖性的Msn2降解。在已显示组成性地将Msn2保留在细胞核中的msn5缺失细胞中，Msn2水平显著降低。这种降解是Srb10依赖性的；在srb10缺失突变体中，Msn2不被降解。一个Msn2内部缺失突变体对Srb10抑制不敏感，但通过Srb10依赖性机制被降解。因此，这种突变使Srb10抑制与降解脱钩。
