Regulation of TFII-I activity by phosphorylation

The transcription factor TFII-I binds to distinct promoter sequences includ ing an initiator element in several eukaryotic genes. Here we demonstrate t hat TFII-I is phosphorylated in vivo at serine/threonine and tyrosine resid ues in the absence of any apparent extracellular signals, This "basal" phos phorylation of TFII-I is not required and does not affect its specific DNA binding, but is critical for its in vitro transcriptional properties via th e V beta promoter. To better assess the functional role of phosphorylation in regulating TFII-I activity, we focused on tyrosine phosphorylation of TF II-I. Ectopically expressed recombinant TFII-I, like its native counterpart , exhibits tyrosine phosphorylation in the absence of distinct extracellula r signals. More important, mutation of a potential consensus tyrosine phosp horylation site in TFII-I leads to severe reduction in its basal transcript ional activation of the V beta promoter in vivo. Taken together, these data suggest that tyrosine phosphorylation of TFII-I is important for its initi ator-dependent transcriptional activity.