Structural and enzymatic characterization of viper C-type virus.

The structural polypeptides of purified viper range in molecular weight from 11,000 to 97,000 daltons and consist of 3 major and about 13 minor polypeptides. The virus contains both protein kinase and reverse transcriptase activities. Several of the structural polypeptides are phosphorylated in vitro by the virus-associated protein kinase. However, most (possibly all) of the viral structural polypeptides are not phosphorylated in vivo. DeoxyATP is as efficient as ATP in donating phosphate for in vitro phosphorylation of viral proteins. In vitro protein phosphorylation always precedes transcription and the virus-associated protein kinase and reverse transcriptase activities can be partially separated by sedimentation in a sucrose gradient.