Overexpression of the gene for Rpb7 subunit of yeast RNA polymerase II rescues the phenotypes associated with absence of the largest, nonessential subunit Rpb4

The easily dissociable subcomplex of Rpb4 and Rpb7 subunits of yeast RNA polymerase II has been considered, for long, to play a role in stabilizing Pol II under stress. On the basis of previous genetic and biochemical observations, it was proposed that within the subcomplex one of the functions of Rpb4p is to stabilize the interaction between Rpb7p and the rest of Pol II. We took a direct approach to test the latter possibility by overexpression and mutagenesis of RPB7 in absence of Rpb4p. We report here the results, which support the latter hypothesis. While it has been previously reported that absence of Rpb4p results in reduction in overall transcription by Pol II, our comparative analysis of RNAs from RPB4 and rpb4 Delta cells suggests that there are indeed several genes differentially expressed between the two cells. We propose that the qualitative differences in overall transcription in presence and absence of Rpb4p imply a more active role for Rpb4p in transcription of at least a subset of genes.