Molecular characterization of the SPT23 gene: a dosage-dependent suppressor of Ty-induced promoter mutations from Saccharomyces cerevisiae.

SPT genes are suppressors of mutations induced by the retrotransposon Ty in Saccharomyces cerevisiae. All SPT genes isolated to date suppress Ty-induced mutations by altering transcription. SPT23 was identified as a multicopy suppressor of the Ty-induced promoter mutations his4-912 delta and lys2-61. Multicopy expression of SPT23 suppresses a variety of Ty-induced promoter mutations, including the MAT-regulated alleles his4-917(480) and lys2-173R2. Here, we report the initial characterization of the SPT23 gene, including its nucleotide sequence and location in the yeast genome. The SPT23 gene contains a 1854 base pair open reading frame. Searches of the current data bases show no homology between SPT23 and previously described genes or proteins. The SPT23 gene is located between RAM2 and MAK11 on the left arm of chromosome XI. Tn10-LUK insertional mutagenesis of the SPT23 gene indicates that SPT23 is not essential for vegetative growth and spt23 mutations do not confer an Spt- phenotype.