engleski

Differential effects of ser to ala mutations in the Gal4 DNA binding domain

The yeast transactivator Gal4 has long served as a paradigm for studies of transcriptional activation in eukaryotes. Gal4 is known to be phosphorylated at several residues throughout the body of the protein including sites within the DNA binding domain which have yet to be precisely mapped. At least two sites, Ser 41 and Ser 47 are potential cdk consensus sites (Ser/Pro). Previous work has shown that cdk8 is required for Gal4 activation via its role in phosphorylating Ser 699. To investigate the potential role of serine phosphorylation in the Gal4 DNA binding domain we systematically mutagenized seven serines to alanine in the Gal4 DNA binding domain. Assaying transcriptional activation in vivo we found that several of the Ser to Ala mutants showed decreased transcriptional activation including Ser5, Ser22, Ser41, Ser47 and Ser85. We next examined the effect of these mutations on DNA binding in vitro and in vivo. EMSA assays showed that several of the mutants exhibit increased DNA binding activity in vitro relative to the wild type protein. Using CHIP assays we show that mutants exhibit a differential ability to bind the Gal4 UAS site in vivo. Since at least some of the serine residues mutagenized in this study lie on the outer surfaces of the Gal4-DNA co-crystal structure and appear not to be involved in DNA binding directly, we surmise that the effects we see may indicate the presence of interactions with other factors at these positions.

Gal4; transcription

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