Processed enzymatically active protease (p15 gag) of avian retrovirus obtained in an E. coli system expressing a recombinant precursor (Pr25 lac-Δgag)

Processing proteases of avian and mammalian retroviruses cut the polyprotein precursors encoded by the retroviral genes into mature functional proteins. Retroviral processing proteases are still a rather poorly characterized group as to their relation to other proteases, specificity, and mechanism of enzymatic action. In avian retroviruses the generation of the processing protease itself comprises a processing cleavage event — the protease p15 gag is cut off the carboxy-terminus of a gag polyprotein precursor, Pr76 gag . We report here that direct and efficient production of the avian retrovirus processing protease p15 gag (required for structure-function studies and rational design of inhibitors) was obtained in an E. coli system, where massive expression of a size-reduced, recombinant precursor (Pr25 lac-Δgag was accompanied by its structurally accurate processing.