The products of the SPT10 and SPT21 genes of Saccharomyces cerevisiae increase the amplitude of transcriptional regulation at a large number of unlinked loci

The 3' long terminal repeat (LTR) of yeast transposon Ty1 is not normally used as a promoter, although it contains sequences identical to those found in the 5' LTR, which does act as a promoter. We have isolated mutations that fall into two genes, SPT10 and SPT21, that allow the 3' LTRs of Ty1 elements inserted at various positions in the genome of Saccharomyces cerevisiae to act as promoters. We find that mutations in these two genes alter transcriptional regulation of Ty1 LTRs and also of certain non-Ty1-related promoters in two ways: (i) they allow the low-level expression of several genes under repressing conditions, and (ii) they allow transcription from the 5' LTR of Ty1 elements in the absence of a normally required activator, SPT3. Furthermore, the fully induced levels of transcription of several genes are reduced in these spt mutants. Hence, the products of these two genes increase the amplitude of transcriptional regulation of a wide variety of unlinked loci.