Isolation and cloning of four subunits of a fission yeast TFIIIC complex that includes an ortholog of the human regulatory protein TFIIIC beta

Eukaryotic tRNA genes are controlled by proximal and downstream elements th at direct transcription by RNA polymerase (pol) III. Transcription factors (TFs) that reside near the initiation site are related in Saccharomyces cer evisiae and humans, while those that reside at or downstream of the B box s hare no recognizable sequence relatedness. Human TFIIIC beta is a transcrip tional regulator that exhibits no homology to S. cerevisiae sequences on it s own. We cloned an essential Schizosaccharomyces pombe gene that encodes a protein, Sfc6p, with homology to the S. cerevisiae TFIIIC subunit, TFC6p, that extends to human TFIIIC beta. We also isolated and cloned S. pombe hom ologs of three other TFIIIC subunits, Sfc3p, Sfc4p, and Sfc1p, the latter t wo of which are conserved from S. cerevisiae to humans, while the former sh ares homology with the S. cerevisiae B box-binding homolog only. Sfc6p is a component of a sequence-specific DNA-binding complex that also contains th e B box-binding homolog, Sfc3p. Immunoprecipitation of Sfc3p further reveal ed that Sfc1p, Sfc3p, Sfc4p, and Sfc6p are associated in vivo and that the isolated Sfc3p complex is active for pol III-mediated transcription of a S. pombe tRNA gene in vitro. These results establish a link between the downs tream pol III TFs in yeast and humans.