Mechanistic implications from the structure of a catalytic fragment of Moloney murine leukemia virus reverse transcriptase

Reverse transcriptase (RT) converts the single-stranded RNA genome of a retrovirus into a double-stranded DNA copy for integration into the host genome. This process requires ribonuclease H as well as RNA- and DNA-directed DNA polymerase activities. Although the overall organization of HIV-1 RT is known from previously reported crystal structures, no structure of a complex including a metal ion, which is essential for its catalytic activity, has been reported.Here we describe the structures at 1.8 Angstrum resolution of a catalytically active fragment of RT from Moloney murine leukemia virus (MMLV) and at 2.6 Angstrum of a complex of this fragment with Mn2+ coordinated in the polymerase active site. On the basis of similarities with HIV-1 RT and rat DNA polymerase beta, we have modeled template/primer and deoxyribonucleoside 5'-triphosphate substrates into the MMLV RT structure.Our model, in the context of the disposition of evolutionarily conserved residues seen here at high resolution, provides new insights into the mechanisms of catalysis, fidelity, processivity and discrimination between deoxyribose and ribose nucleotides.