DNA-REPAIR GENE RAD3 OF SACCHAROMYCES-CEREVISIAE IS ESSENTIAL FOR TRANSCRIPTION BY RNA POLYMERASE-II

THE RAD3 gene of Saccharomyces cerevisiae is required for excision rep air of ultraviolet-damaged DNA and is essential for cell viability1. T he RAD3-encoded protein shares a high degree of homology with the huma n ERCC2(XPD) gene product2. Mutations in XPD, besides causing the canc er-prone syndrome xeroderma pigmentosum, can also result in Cockayne's syndrome and trichothiodystrophy3. To investigate the role of RAD3 in viability, we examine here the effect of a recessive, temperature-sen sitive (ts) conditional lethal mutation of the gene on transcription b y RNA polymerase II. Upon transfer to the restrictive temperature, the rad3-ts mutant rapidly ceases growth and poly(A)+ RNA synthesis is in hibited drastically. Messenger RNA levels of all the genes examined, H IS3, TRP3, STE2, MET19, RAD23, CDC7, CDC9 and ACT1, decline rapidly up on loss of RAD3 activity. The synthesis of heat-shock-inducible HSP26 mRNA and galactose-inducible GAL7 and GAL10 mRNAs is also drastically inhibited in the rad3-ts mutant at the restrictive temperature. The RN A polymerase II transcriptional activity in extract from the rad3-ts14 strain is thermolabile, and this in vitro transcriptional defect can be fully corrected by the addition of homogeneous RAD3 protein. These findings indicate that RAD3 protein has a direct and essential role in RNA polymerase II transcription.