MUTATIONS IN RNA-POLYMERASE-II AND ELONGATION-FACTOR SII SEVERELY REDUCE MESSENGER-RNA LEVELS IN SACCHAROMYCES-CEREVISIAE

Elongation factor SII interacts with RNA polymerase II and enables it to transcribe through arrest sites in vitro. The set of genes dependen t upon SII function in vivo and the effects on RNA levels of mutations in different components of the elongation machinery are poorly unders tood. Using yeast lacking SII and bearing a conditional allele of RPB2 , the gene encoding the second largest subunit of RNA polymerase II, w e describe a genetic interaction between SII and RPB2. An SII gene dis ruption or the rpb2-10 mutation, which yields an arrest-prone enzyme i n vitro, confers sensitivity to 6-azauracil (6AU) a drug that depresse s cellular nucleoside triphosphates. Cells with both mutations had red uced levels of total poly(A)(+) RNA and specific mRNAs and displayed a synergistic level of drug hypersensitivity. In cells in which the SII gene was inactivated, rpb2-10 became dominant, as if template-associa ted mutant RNA polymerase II hindered the ability of wild-type polymer ase to transcribe. Interestingly, while 6AU depressed RNA levels in bo th wild-type and mutant cells, wild-type cells reestablished normal RN A levels, whereas double-mutant cells could not. This work shows the i mportance of an optimally functioning elongation machinery for in vivo RNA synthesis and identifies an initial set of candidate genes with w hich SII-dependent transcription can be studied.