Tfg3, a subunit of the general transcription factor TFIIF in Schizosaccharomyces pombe, functions under stress conditions.

TFIIF is a general transcription factor (GTF) that binds to RNA polymerase II (pol II) for subsequent recruitment of pol II to a promoter. TFIIF of Saccharomyces cerevisiae contains a small subunit, designated Tfg3, in addition to two conserved subunits, TFIIFalpha (Tfg1) and TFIIFbeta (Tfg2). In this study, we characterized Tfg3 of Schizosaccharomyces pombe. Using Tfg3 fused to green fluorescent protein (GFP), we found that Tfg3 is located in nuclei, and it is assembled into the C-terminal domain phosphatase (Fcp1)/TFIIF/pol II complex via interactions with TFIIFalpha and TFIIFbeta. As in the case of S.cerevisiae, Tfg3 in S.pombe forms part of another GTF, namely TFIID. The TFIID complex isolated from S.pombe that had been cultured at elevated temperatures included increased levels of Tfg3. The interaction of recombinant Tfg3 with TATA-binding protein (TBP), the central subunit of TFIID, was temperature-dependent. Moreover, a mutant of S.pombe that lacked the gene for Tfg3 was sensitive to a battery of stresses including temperature up-shift. Starting from a mutant with tfg3- mutation, we isolated five species of multicopy suppressors. Expression levels of the suppressor genes were lower in the mutant cell than in wild-type cell at an elevated temperature. Taken together, we propose that Tfg3 is involved in transcriptional regulation under stress conditions, in particular, at high temperatures.

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