Mutational analysis of the DNA polymerase and ribonuclease H activities of human immunodeficiency virus type 2 reverse transcriptase expressed in Escherichia coli.

We have constructed a plasmid that, when introduced into Escherichia coli, induces the synthesis of large quantities of a polypeptide with an apparent molecular weight of 68 kDa. The HIV-2 reverse transcriptase (RT) made in E. coli is soluble in bacterial extracts and possesses both RNA-dependent DNA polymerase and ribonuclease H (RNase H) activities typical of retroviral RTs. The HIV-2 RT expression clone was used to generate mutations in HIV-2 RT. There is a strong correlation between the effects of individual mutations on the DNA polymerase and RNase H activities. Mutations that profoundly affect the two catalytic functions are not clustered in any particular region of the polypeptide. Those few mutations that selectively affect either the RNase H or the DNA polymerase suggest that, like other retroviral RTs, the DNA polymerase is associated with the amino-terminal portion of HIV-2 RT and the RNase H with the carboxy-terminal portion. Genetically, the HIV-2 RT resembles the HIV-1 RT more closely than it resembles Moloney murine leukemia virus RT. The two catalytic functions of Moloney murine leukemia virus RT can be separately expressed in active form by molecular cloning; those of HIV-1 and HIV-2 RT cannot.