The Saccharomyces cerevisiae RuvB-like protein, Tih2p, is required for cell cycle progression and RNA polymerase II-directed transcription

Two highly conserved RuvB-like putative DNA helicases, p47/TIP49b and p50/T IP49a, have been identified in the eukaryotes. Here, we study the function of Saccharomyces cerevisiae TIH2, which corresponds to mammalian p47/TIP49b . Tih2p is required for vegetative cell growth and localizes in the nucleus , Immunoprecipitation analysis revealed that Tih2p tightly interacts with T ih1p, the counterpart of mammalian p50/TIP49a, which has been shown to inte ract with the TATA-binding protein and the RNA polymerase II holoenzyme com plex. Furthermore, the mutational study of the Walker A motif, which is req uired for nucleotide binding and hydrolysis, showed that this motif plays i ndispensable roles in the function of Tih2p, When a temperature-sensitive t ih2 mutant, tih2-160, was incubated at the nonpermissive temperature, cells were rapidly arrested in the G(1) phase. Northern blot analysis revealed t hat Tih2p is required for transcription of G(1) cyclin and of several ribos omal protein genes. The similarities between the mutant phenotypes of tih2- 160 and those of taf145 mutants suggest a role for TIH2 in the regulation o f RNA polymerase II-directed transcription.