Molecular and genetic characterization of SPT4, a gene important for transcription initiation in Saccharomyces cerevisiae.

Mutations in the SPT4 gene of Saccharomyces cerevisiae were isolated as suppressors of delta insertion mutations that interfere with adjacent gene transcription. Recent genetic evidence indicates that the SPT4 protein functions with two other proteins, SPT5 and SPT6, in some aspect of transcription initiation. In this work we have characterized the SPT4 gene and we demonstrate that spt4 mutations, like spt5 and spt6 mutations, cause changes in transcription. Using the cloned SPT4 gene, spt4 null mutations were constructed; in contrast to spt5 and spt6 null mutants, which are inviable, spt4 null mutants are viable and have an Spt- phenotype. The DNA sequence of the SPT4 gene predicts a protein product of 102 amino acids that contains four cysteine residues positioned similarly to those of zinc binding proteins. Mutational analysis suggests that at least some of these cysteines are essential for SPT4 function. Genetic mapping showed that SPT4 is a previously unidentified gene that maps to chromosome VII, between ADE6 and CLY8.