Casein kinase II enhances the DNA binding activity of serum response factor.
Serum response factor (SRF) is a mammalian transcription factor that binds to the serum response element in the enhancer of the c-fos proto-oncogene and thus may mediate serum-induction of c-fos transcription. We report here that the DNA binding activity of recombinant SRF made in Escherichia coli can be greatly enhanced by incubation of the protein with HeLa cell nuclear extract. The enhancing activity is ATP or GTP dependent and cofractionates with a protein kinase that phosphorylates SRF on a specific tryptic peptide. Coincubation with phosphatase blocks the enhancing activity, further suggesting that the enhanced binding activity is due to phosphorylation. The specific tryptic phosphopeptide phosphorylated in vitro is also phosphorylated in vivo, demonstrating that this phosphorylation is physiologically important. We have localized the phosphorylation site by a small deletion mutant. Finally, we show that the kinase activity is provided by casein kinase II (CKII) or a close variant. The potential role of CKII as either a regulatory or constitutive modifier of SRF in vivo will be discussed.
Department of Biological Sciences, Columbia University, New York, New York 10027.
J R
JR
Manak
N
N
de Bisschop
R M
RM
Kris
R
R
Prywes
D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D047388:Casein Kinases; D002457:Cell Extracts; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D026362:Serum Response Factor; D014158:Transcription, Genetic
D002457:Cell Extracts; D004268:DNA-Binding Proteins; C000715470:MAS1 protein, human; D009687:Nuclear Proteins; D000090063:Proto-Oncogene Mas; D026362:Serum Response Factor; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D004247:DNA; D011494:Protein Kinases; D047388:Casein Kinases