THE 68-KDA CALMODULIN-BINDING PROTEIN IS TIGHTLY ASSOCIATED WITH THE MULTIPROTEIN DNA-POLYMERASE ALPHA-PRIMASE COMPLEX IN HELA-CELLS

Calcium and its receptor protein calmodulin function in the regulation of proliferation of mammalian cells. A 68 kDa calmodulin-specific bin ding protein was shown previously to be associated with growth factor- dependent progression of a variety of mammalian cells from G1 to S pha se and to stimulate DNA synthesis in permeabilized hematopoietic proge nitor cells, In this report we show that the 68 kDa calmodulin-specifi c binding protein in HeLa cells is tightly associated with the DNA pol ymerase a-primase component of the 21S complex of enzymes for DNA synt hesis. The 68 kDa calmodulin-binding protein and the DNA polymerase cr -primase complex cofractionate during Q-Sepharose chromatography to is olate the 21S enzyme complex, native and denatured DNA-cellulose to di ssociate the 21S complex, and DEAE-Bio-Gel chromatography to isolate t he multiprotein DNA polymerase cc-primase complex. The 68 kDa calmodul in-specific binding protein and DNA polymerase or also bind and coelut e during affinity chromatography on calmodulin-agarose. They also copr ecipitate with C10-agarose-linked monoclonal antibody SJK 132-20 to hu man DNA polymerase or. The tight association of the 68 kDa calmodulin- binding protein to the DNA polymerase alpha-primase complex supports a function for this protein in the regulation of DNA synthesis in vivo.