GC box binding induces phosphorylation of Sp1 by a DNA-dependent protein kinase

Cell. 1990 Oct 5;63(1):155-65. doi: 10.1016/0092-8674(90)90296-q.


Efficient transcription of SV40 early genes requires transcription factor Sp1. Here, we report that SV40 infection induces Sp1 phosphorylation. While characterizing this modification, we discovered that Sp1 becomes quantitatively phosphorylated in an in vitro transcription extract. Multiple processive phosphorylation of Sp1 depends on binding of Sp1 to GC box-containing DNA. Cell fractionation and column chromatography reveal that the Sp1 kinase is a nuclear DNA binding protein that corresponds to a previously identified DNA-dependent protein kinase. Because only some trans-activators are phosphorylated by this kinase, Sp1 belongs to a specific subgroup of factors that are phosphorylated upon binding to promoter sequences. Finally, efficient phosphorylation of Sp1 requires both a functional DNA binding domain and a region containing the transcriptional activation domains. Coupling of phosphorylation to DNA binding may represent a novel mechanism for regulating transcriptional initiation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Cell Line
  • Cell Nucleus / enzymology
  • Cell Transformation, Viral
  • HeLa Cells / metabolism
  • Humans
  • Phosphorylation
  • Protein Kinases / isolation & purification
  • Protein Kinases / metabolism*
  • Simian virus 40 / genetics*
  • Sp1 Transcription Factor / genetics
  • Sp1 Transcription Factor / isolation & purification
  • Sp1 Transcription Factor / metabolism*
  • Substrate Specificity
  • Transcription, Genetic


  • Sp1 Transcription Factor
  • Protein Kinases
  • Sp1 kinase