DSIF, a novel transcription elongation factor that regulates RNA polymerase II processivity, is composed of human Spt4 and Spt5 homologs
- Tadashi Wada,
- Toshiyuki Takagi,
- Yuki Yamaguchi,
- Anwarul Ferdous,
- Takeshi Imai,
- Susumu Hirose,
- Seiji Sugimoto,
- Keiichi Yano,
- Grant A. Hartzog,
- Fred Winston,
- Stephen Buratowski, and
- Hiroshi Handa
- Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama 226, Japan; National Institute of Genetics, Mishima, Shizuoka-ken 411, Japan; Tokyo Research Laboratories, Kyowa Hakko Kogyo Co., Ltd., Machida-shi 194, Japan; Department of Genetics and Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115 USA
Abstract
We report the identification of a transcription elongation factor from HeLa cell nuclear extracts that causes pausing of RNA polymerase II (Pol II) in conjunction with the transcription inhibitor 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB). This factor, termed DRBsensitivity-inducing factor (DSIF), is also required for transcription inhibition by H8. DSIF has been purified and is composed of 160-kD (p160) and 14-kD (p14) subunits. Isolation of a cDNA encoding DSIF p160 shows it to be a homolog of the Saccharomyces cerevisiae transcription factor Spt5. Recombinant Supt4h protein, the human homolog of yeast Spt4, is functionally equivalent to DSIF p14, indicating that DSIF is composed of the human homologs of Spt4 and Spt5. In addition to its negative role in elongation, DSIF is able to stimulate the rate of elongation by RNA Pol II in a reaction containing limiting concentrations of ribonucleoside triphosphates. A role for DSIF in transcription elongation is further supported by the fact that p160 has a region homologous to the bacterial elongation factor NusG. The combination of biochemical studies on DSIF and genetic analysis of Spt4 and Spt5 in yeast, also in this issue, indicates that DSIF associates with RNA Pol II and regulates its processivity in vitro and in vivo.
