The Kluyveromyces gene encoding the general transcription factor IIB: structural analysis and expression in Saccharomyces cerevisiae.

The Kluyveromyces lactis gene encoding the general transcription factor IIB (TFIIB) was isolated from a genomic library by complementation of the cold-sensitive phenotype conferred by a mutation in the SUA7 gene, which encodes TFIIB in Saccharomyces cerevisiae. DNA sequence analysis of the KI-SUA7 gene revealed a 357 amino acid open reading frame that is 67% identical (81% overall similarity) to S. cerevisiae TFIIB. Comparison with other eukaryotic TFIIBs indicated that the most highly conserved sequence is located adjacent to the Zn-finger motif near the N-terminus. A plasmid shuffle system was used to replace the essential Sc-SUA7 gene with KI-SUA7 in S.cerevisiae. The resulting strain was viable and phenotypically indistinguishable from the normal strain. However, transcription start site selection at the ADH1 locus, shown previously to be affected by mutations in Sc-SUA7, was affected by K.lactis TFIIB. This result provides further evidence that TFIIB is a principal determinant of start site selection in yeast.