C‐terminal phosphorylation of the serum‐response factor

Abstract

The serum‐response factor (SRF) is essential for the induction and repression of the protooncogene c‐fos. Phosphorylation of SRF has been implicated to be involved in these processes and five phosphorylation sites have already been mapped within the N‐terminal region. Here we show that in vivo additional phosphorylation of SRF does occur. This modification is located primarily within amino acids 206–289, which probably contain more than one phosphorylation site. Microsequencing allowed the identification of one phosphorylation site at Ser253, which is a potential target of casein kinase II. Mutational analysis revealed that, in contrast to N‐terminal phosphorylation, Ser253 phosphorylation does not affect DNA‐binding properties. In addition, phosphorylation at Ser253 does not seem to change transactivation activity of SRF but rather influences its contribution to transcriptional repression. Thus, C‐terminal phosphorylation of SRF may modulate c‐fos basal repression. Copyright © 1993, Wiley Blackwell. All rights reserved