Characterization of the reverse transcriptase of a type C RNA virus produced by a human lymphoma cell line

The reverse transcriptase (RNA-dependent DNA nucleotidyltransferase) of the type C RNA virus produced by the human lymphoma cell line SU-DHL-1 was purified by ion-exchange chromatography of SU-DHL-1 culture fluids and repetitive affinity chromatography on poly(rC).agarose, as were the polymerases of several other type C viruses. The DHL-1 enzyme used template-primers at levels expected of a viral reverse transcriptase, and sodium dodecyl sulfate gel electrophoretic analysis of radioiodinated DHL-1 enzyme revealed a peak at a position corresponding to those of several other type C viral reverse transcriptases (namely, at 72,000-78,000 daltons). The purified enzyme was partially neutralized by antibodies specific for the reverse transcriptase of simian sarcoma virus. Two-dimensional analysis on thin-layer cellulose plates of tryptic hydrolysates of the radioiodinated enzymes of several viruses revealed that six peptides are common to the polymerases of simian sarcoma virus, gibbon ape leukemia virus, baboon endogenous virus, and the DHL-1 virus, and that two to four peptides are unique to each of these enzymes. The DHL-1 viral reverse transcriptase appears to be most closely related structurally to the enzymes of simian sarcoma virus, gibbon ape leukemia virus, and baboon endogenous virus. However, the DHL-1 viral enzyme differed from any one or combination of the other subhuman primate viral enzymes by virtue of its unique peptides. The implications of these findings with respect to the probable origin of the DHL-1 virus are discussed.