PROTEOLYTIC RELEASE AND CRYSTALLIZATION OF THE RNASE-H DOMAIN OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 REVERSE-TRANSCRIPTASE

The RNase H domain of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase was released from recombinant DHFR-RNase H fusion protein by the action of HIV-1 protease and crystallized as large trigonal prisms that diffract x-rays to at least 2.4-angstrom resolution. The protease cleavage occurred 18 residues away from the Phe440-Tyr441 site reported to be processed during maturation of the reverse transcriptase heterodimer. Mutagenesis of the protease-sensitive region (residues 430-440), which is part of the crystallized domain, indicates that any alteration of the wild-type sequence results in increased proteolysis of the p66 subunit. A model of asymmetric processing in HIV-1 reserve transcriptase which involves partial unfolding of the RNase H domain is proposed based on these results and the recently reported three-dimensional structure of this domain.