A CHIMERIC SUBUNIT OF YEAST TRANSCRIPTION FACTOR IIIC FORMS A SUBCOMPLEX WITH TAU-95

The multisubunit yeast transcription factor IIIC (TFIIIC) is a multifu nctional protein required for promoter recognition, transcription fact or IIIB recruitment, and chromatin antirepression. We report the isola tion and characterization of TFC7, an essential gene encoding the 55-k Da polypeptide, tau 55, present in affinity-purified TFIIIC. tau 55 is a chimeric protein generated by an ancient chromosomal rearrangement. Its C-terminal half is essential for cell viability and sufficient to ensure TFIIIC function in DNA binding and transcription assays. The N -terminal half is nonessential and highly similar to a putative yeast protein encoded on another chromosome and to a cyanobacterial protein of unknown function. Partial deletions of the N-terminal domain impair ed tau 55 function at a high temperature or in media containing glycer ol or ethanol, suggesting a link between PolIII transcription and meta bolic pathways. Interestingly, tau 55 was found, together with TFIIIC subunit tau 95, in a protein complex which was distinct from TFIIIC an d which may play a role in the regulation of PolIII transcription, pos sibly in relation to cell metabolism.