Abstract
An RNA-directed DNA polymerase was associated with intracytoplasmic A-particles from DBA/2 mouse leukemia cells. The enzyme activity was detected after disrupting the purified particles with 2 M NaCl-20 mM dithiothreitol. The presence of a divalent cation and all 4 deoxyribonucleoside triphosphates was essential for this enzyme activity. The enzyme had a clear preference for Mg2+ over Mn2+. Cs2SO4 isopycnic gradient centrifugation of the DNA product synthesized in the actinomycin D-containing reaction revealed the presence of DNA-RNA hybrid. The purified DNA product hybridized with RNA isolated from A-particles. The endogenous A-particle RNA apparently serves as the template for the DNA polymerase.