Purification and Properties of RNA‐Dependent DNA Polymerase from Cytoplasmic A‐Type Particles of Murine Mammary Tumor Virus

Publisher Website
Google Scholar
Abstract
The RNA‐dependent DNA polymerase associated with cytoplasmic A‐type particles of murine mammary tumor virus was isolated to near homogeneity by a procedure which includes dissociation of proteins from RNA by centrifugation in a step gradient of cesium chloride, followed by an affinity chromatography on poly(rC)‐agarose column. Two species of DNA polymerase were separated by the chromatography: enzyme I in 0.55 M NaCl and enzyme II in 0.80 M NaCl eluate, respectively. The purified DNA polymerases consist of two major polypeptides, with molecular weights of 94000 and 42000, as the intrinsic subunits. Both enzyme protomers with a sedimentation coefficient of 6.3–6.4 S and a molecular weight of 115000–120000 associate to form active oligomers in low‐ionic‐strength buffer. Both enzymes catalyzed the hydrolysis of RNA in RNA. DNA hybrids as well as the RNA‐dependent synthesis of DNA; these are the intrinsic activities of the reverse transcriptase from B‐type particles of murine mammary tumor virus as well as from avian and mammalian C‐type oncornaviruses. The general catalytic properties are similar to those of the enzyme from B‐type particles. Compared with DNA polymerases I, DPU'A polymerase II exhibited a high affinity for all the template‐primers tested and, in addition, a high preference for (rC)n· (dG)12–18.