A PORTION OF RNA POLYMERASE-II MOLECULES HAS A COMPONENT ESSENTIAL FOR STRESS RESPONSES AND STRESS SURVIVAL

Cells respond to stress by altering gene expression, and these adjustm ents facilitate stress tolerance. Although transcriptional changes are integral to most stress responses, little is known about the mechanis ms that permit the transcription apparatus itself to tolerate stress. Here we report that a major role of the RNA polymerase II subunit RPB4 is to permit appropriate transcriptional responses during stress. Yea st cells lacking RPB4 have essentially wild-type growth rates at moder ate temperatures (18 to 22-degrees-C), but their growth rates are subs tantially reduced at temperatures outside this range. When subjected t o a heat shock, cells lacking RPB4 rapidly lose the ability to transcr ibe genes and experience a dramatic loss in viability. When cells lack ing RPB4 are subjected to the nutrient stress that accompanies entry i nto stationary phase, they also exhibit a substantial decline in mRNA synthesis and in viability relative to wild-type cells. Interestingly, the portion of RNA polymerase II molecules that contain RPB4 is small in log phase but increases substantially as cells enter stationary ph ase. We propose that the association of RPB4 with the other RNA polyme rase II subunits increases the tolerance of the enzyme to stress.