Phosphorylation of the high‐mobility‐group‐like protein P1 by casein kinase‐2

Abstract

The nuclear protein P1 (molecular mass 53 kDa), found in all mammalian cell types and tissues so far tested, is an excellent substrate for casein kinase-2. The number of phosphate groups on P1 is 20-30/molecule; the phosphorylation sites are distributed throughout the molecule. The phosphate is present as serine phosphate and possibly threonine phosphate. Proteolytic digestion with Staphylococcus aureus V8 protease of 32P-labelled P1 both in vivo and in vitro revealed that casein kinase-2 may be one of the kinases responsible for the phosphorylation in vivo.