ISOLATION OF TFC1, A GENE ENCODING ONE OF 2 DNA-BINDING SUBUNITS OF YEAST TRANSCRIPTION FACTOR-TAU (TFIIIC)

Transcription factor TFIIIC mediates tRNA and 5S RNA gene activation by binding to intragenic promoter elements. The factor from Saccharomyces cerevisiae, also called tau, is a large, multisubunit protein (550-650 kDa) containing two polypeptides that interact directly with DNA encoding tRNA (tDNA). We have obtained peptide sequences from the 95-kDa DNA-binding subunit (tau-95) and cloned the corresponding gene, called TFC1. The gene encodes a polypeptide of calculated M(r) 73,500. However, when TFC1 was transcribed and translated in vitro, the gene product comigrated with tau-95 in SDS/polyacrylamide gels. A fusion protein expressed in bacteria was able to prevent the binding of anti-tau-95 antibodies to tau-tDNA complexes. The TFC1 gene is present in single copy on yeast chromosome II and is essential for growth. Spores containing a disrupted gene germinate but only proceed through a few cell divisions before ceasing to grow. The TFC1-encoded protein contains a potential helix-turn-helix structure and an acidic carboxyl-terminal domain, a feature characteristic of some DNA-binding proteins and transcriptional regulators.