Casein kinase II inhibits the DNA-binding activity of Max homodimers but not Myc/Max heterodimers.
Max is a heterodimeric partner of the Myc oncoprotein with sequence-specific DNA-binding activity. We found that the DNA-binding activity of bacterially expressed Max homodimers was inhibited in an ATP-dependent reaction by phosphorylation in vitro with purified bovine casein kinase II (CKII). In contrast, phosphorylation of Max and/or Myc by CKII had no inhibitory or stimulatory effect on the DNA-binding activity of Myc/Max heterodimers. By deletion analysis and site-directed mutagenesis, the inhibitory domain was localized to a CKII phosphorylation site in the amino terminus of Max. Finally, extracts prepared from NIH-3T3 cell lines that overexpress Max contained a phosphorylated Max protein which, following phosphatase treatment or heterodimerization with Myc, was capable of sequence-specific DNA-binding activity. Immunoprecipitation experiments confirmed that Max was also phosphorylated in NIH-3T3 cells, demonstrating that Max phosphorylation may have an important physiological function.
Berberich
S J
SJ
Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, New Jersey 08544-1014.
Cole
M D
MD
D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D047390:Casein Kinase II; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014157:Transcription Factors
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; C067850:Myc associated factor X; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; C068422:Max protein, mouse; D000255:Adenosine Triphosphate; D004247:DNA; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases