Isolation and Characterization of the SPT2 Gene, a Negative Regulator of Ty-Controlled Yeast Gene Expression

Abstract

The his4-917 mutation of Saccharomyces cerevisiae results from the insertion of the Ty element Ty917 into the regulatory region of the HIS4 gene and renders the cell His⁻. The hist4-912δ mutant, which carries a solo δ in the 5′-noncoding region of HIS4, is His⁺ at 37°C but His⁻ at 23°C. Both these mutations interfere with HIS4 expression at the transcriptional level. The His⁻ phenotype of both insertion mutations is suppressed by mutations at the SPT2 locus. The product of the wild-type SPT2 gene apparently represses HIS4 transcription in these mutant strains; this repression is relieved when the SPT2 gene is destroyed by mutation. The repression of transcription by SPT2 presumably results from an interaction between the SPT2⁺ gene product and Ty or δ sequences. In this paper, we report the cloning and DNA sequence analysis of the wild-type SPT2 gene and show that the gene is capable of encoding a protein of 333 amino acids in length. In addition, we show that a dominant mutation of the SPT2 gene results from the generation of an ochre codon which is presumed to lead to a shortened SPT2 gene product.