PURIFIED YEAST RNA POLYMERASE-II READS THROUGH INTRINSIC BLOCKS TO ELONGATION IN RESPONSE TO THE YEAST TFIIS ANALOG, P37

Saccharomyces cerevisiae has a TFIIS-related transcription elongation factor, originally called P37 (Sawadogo, M., Sentenac, A., and Fromage ot, P. (1979) J. Biol. Chem. 255, 12-15; Nakanishi, T., Nakano, A., No mura, K., Sekimizu, K., and Natori, S. (1992) J. Biol. Chem. 267, 1320 0-13204), which binds directly to RNA polymerase II and stimulates rea d-through of intrinsic blocks to elongation. To elucidate functional f eatures of this protein:protein interaction, we tested the ability of several forms of RNA polymerase II to respond to either full-length or an amino-terminal truncation of TFIIS. The variants of the polymerase differed in the structure of the carboxyl-terminal domain of the larg est subunit or lacked two of the smaller subunits. No differences in a bility to recognize intrinsic blocks to elongation or to read through them in response to either form of TFIIS were detected among these var iants. Furthermore, ternary complexes containing each variant form of RNA polymerase cleave the 3' end of the nascent transcripts in respons e to TFIIS, a reaction previously reported for mammalian and Drosophil a TFIIS (Kassavetis, G. A., and Geiduschek, E. P. (1993) Science 259, 944-945) and likely to be important in TFIIS function. Thus the carbox yl-terminal domain of the largest subunit and subunits four and seven of the polymerase, required in vivo, are not required in vitro for rec ognition of intrinsic blocks to elongation, read-through in response t o TFIIS, or TFIIS-stimulated cleavage of the nascent transcript.