Effect of calcium on the recovery and distribution of DNA polymerase α from cultured human cells

It was recently reported that the extraction of regenerating rat liver in solutions of isotonic sucrose containing 4 mM CaCl₂ leads to almost quantitative recovery of DNA polymerase α activity in the purified nuclear compartment. Our application of this method to the isolation of the DNA polymerase activities from cultured human epithelial and lymphoblastoid cells has led to substantially different results. We have observed that the inclusion of Ca²⁺ in either isotonic sucrose or hypotonic aqueous extraction media leads to the irreversible inactivation of the majority, cytoplasmic fraction of DNA polymerase α activity and is without quantitative effect on the recovery of the nuclear fraction of this activity.