Intrinsic activity of precursor forms of HIV‐1 proteinase

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Abstract
The wild-type -Phe*Pro- bond located at the N-terminus of the mature aspartic proteinase of HIV-1 was replaced by -Ile-Pro- or -Val-Pro-. By this means, processing at this cleavage junction was prevented and so, extended or precursor forms of HIV-proteinase were generated. These constructs were expressed in Escherichia coli, purified therefrom, and their specificity, activity at different pH values and susceptibility to the potent inhibitor, Ro31-8959, was assessed. A hitherto unobserved cleavage junction (at ∼Ala-Phe*Leu-Gln∼) in the frame-shift region of the gag-pol viral penome was identified and confirmed by demonstrating cleavage of a synthetic peptide corresponding to this region. The implications for viral replication of self-processing at neutral pH by proteinase whilst still present (in a precursor form) as a component of the polyprotein are considered; such reactions, however, are still blocked even at pH values as high as 8.0 by Ro31-8959.