Yeast SNF2/SWI2, SNF5, and SNF6 proteins function coordinately with the gene-specific transcriptional activators GAL4 and Bicoid.

The SNF2 (SWI2), SNF5, and SNF6 genes are required for transcription of many diversely regulated genes in Saccharomyces cerevisiae. Previously, we showed that SNF2, SNF5, and SNF6 function interdependently in transcriptional activation, possibly forming a heteromeric complex. Here, we present evidence that SNF6 has a more direct role in stimulating transcription than SNF2 and SNF5. The global effects of mutations in SNF2, SNF5, and SNF6 suggested that these SNF proteins may function coordinately with many gene-specific activators. We show that LexA-GAL4 and LexA-Bicoid fusion proteins are both dependent on SNF2, SNF5, and SNF6 for activation of target genes containing one or multiple lexA operators. The stringency of the requirement for the SNF proteins varies with the activator, the number of binding sites for the activator, and the target promoter. Thus, these SNF proteins appear to represent a class of intermediary proteins that facilitate transcriptional activation by gene-specific regulatory proteins.