Rpb4p is necessary for RNA polymerase II activity at high temperature

Rpb4p and Rpb7p are two subunits of the yeast RNA polymerase II, which form a subcomplex that can dissociate from the enzyme in vitro, Whereas RPB7 is essential, RPB4 is dispensable for cellular viability. However, the rpb4 n ull mutant is heat-sensitive, and it has been suggested that Rpb4p is an es sential component for cellular stress response. To examine this hypothesis, we used two-dimensional gel electrophoresis to analyze the protein express ion pattern of the rpb4 null mutant in response to heat shock, oxidative st ress, osmotic stress, and in the post-diauxic phase. We show that this muta nt is not impaired in stress induced transcriptional activation: the absenc e of heat shock response of the mutant is due to a general defect in RNA po lymerase II activity at high temperature. Under this condition, Rpb4p is ne cessary to maintain the polymerase activity in vivo, The heat growth defect of the rpb4 null mutant can be partially suppressed by overexpression of R PB7, suggesting that Rpb4p maintains or stabilizes Rpb7p in the RNA polymer ase, We also demonstrate that rpb4 null mutant is an appropriate tool to an alyze the involvement of transcriptional events in the survival and adaptat ion to heat shock or other stresses.