YEAST NUCLEOTIDE EXCISION-REPAIR PROTEINS RAD2 AND RAD4 INTERACT WITHRNA-POLYMERASE-II BASAL TRANSCRIPTION FACTOR-B (TFIIW)

The Rad2, Rad3, Rad4, and Ss12 proteins are required for nucleotide ex cision repair in yeast cells and are homologs of four human proteins w hich are involved in a group of hereditary repair-defective diseases. We have previously shown that Rad3 protein is one of the five subunits of purified RNA polymerase II basal transcription initiation factor b (TFIIH) and that SsI2 protein physically associates with factor b (W. J. Feaver, J Q. Svejstrup, L. Bardwell, A. J. Bardwell, S. Buratowski, K. D. Gulyas, T. F. Donahue, E. C. Friedberg, and R. D. Kornberg, Cel l 75:1379-1387, 1993). Here we show that the Rad2 and Rad4 proteins in teract with purified factor b in vitro. Rad2 (a single-stranded DNA en donuclease) specifically interacts with the Tfb1 subunit of factor b, and we have mapped a limited region of the Rad2 polypeptide which is s ufficient for this interaction. Rad2 also interacts directly with Ss12 protein (a putative DNA helicase). The binding of Rad2 and Rad4 prote ins to factor b may define intermediates in the assembly of the nucleo tide excision repair repairosome. Furthermore, the loading of factor b (or such intermediates) onto promoters during transcription initiatio n provides a mechanism for the preferential targeting of repair protei ns to actively transcribing genes.