Studies on the DNA polymerase activity contained in particles released from human embryo cell monolayers

Cell monolayers derived from a whole human embryo released particles when grown at 39°C, but not at 36°C, that had RNAase and actinomycin D-sensitive endogenous DNA polymerase activity which banded in sucrose density gradients at 1.17 g/cm³. Monolayers from embryonic skin and muscle, kidney and lung also released such particles. The release phenomenon appears to be spespecific to human embryonic cells, since similar endogenous DNA polymerase activity could not be detected in culture fluid from several established human cell lines of different origin grown at 39°C. DNA polymerase activity purified from these human embryo particles by salt and neutral detergent extraction, followed by DEAE-cellulose and phosphocellulose chromatography (i) had a molecular weight of 105000 as determined by Sephadex G-200 gel filtration; (ii) copied activated calf thymus DNA most efficiently among the template-primers tested and poly(dC) · (dG)_12-18 much less effectively, and did not respond to poly(A) · (dT)_12-18 or (dT)_12-18 alone; (iii) was not inhibited by N-ethylmaleimide at a concentration of 1 · 10^-3 M; and (iv) was stimulated by the presence of KCl in reaction mixtures up to a concentration of 70 mM. The DNA polymerase from the human embryo particles does not therefore possess the properties of viral RNA-directed DNA polymerase, even though the particles themselves exhibit several of the properties of an RNA tumor virus. Moreover, all properties determined for the human embryo enzyme were similar or identical to those of human mitochondrial DNA polymerase (Fry, M. and Weissbach, A. (1973) Biochemistry 12, 3602-3608).