GAL4 is phosphorylated as a consequence of transcriptional activation.

GAL4 protein isolated from yeast in which it is active is phosphorylated predominantly on two different serine residues. One of these was identified as Ser-837; substitution of this residue for alanine has no detectable effect on transcriptional activation by GAL4. Phosphorylation at Ser-837 requires that both the DNA binding and transcriptional activation functions be intact. We propose that some phosphorylations of GAL4, including that at Ser-837, occur concomitantly with activation of transcription.