Binding of the DNA polymerase alpha-DNA primase complex to the nuclear matrix in HeLa cells

It is well-known that there are multiple forms of DNA polymerase alpha. In order to determine which form(s) is (are) tightly bound, the activities were dissociated from DNA-poor nuclear matrices, with octyl beta-D-glucoside. Sucrose gradient sedimentation analysis revealed three bands with s values of 7.5, 10.5, and 13. The 7.5S form was free of DNA primase and represented only 10% of the total DNA polymerase alpha bound to the nuclear matrix. The 13S and the 10.5S forms each contained DNA primase activity. The 10.5S form comprised 85% of the DNA polymerase alpha activity and 95% of the DNA primase activity, dissociated from the nuclear matrix. Neither temperature of nuclease digestion nor various salt treatments of nuclei had significant effects on the proportions of DNA polymerase alpha and DNA primase activities bound to, or subsequently dissociated from, nuclear matrices. In a comparison of primase activity bound to the nuclear matrix, dissociated from the nuclear matrix, and in the soluble fraction, it was found that the bound activity had a lower ATP dependence, had less KCl inhibition, and was less sensitive to heat, compared to the dissociated and soluble activities. No differences in Mg2+ or pH dependence were noted. The amounts of DNA polymerase alpha and DNA primase activities bound to the nuclear matrix varied over the cell cycle of synchronized cells. Over the S phase, there were two peaks of matrix-bound DNA primase and two peaks of subsequently dissociated DNA polymerase alpha-DNA primase complex.(ABSTRACT TRUNCATED AT 250 WORDS)