AVIAN-SARCOMA LEUKEMIA-VIRUS PROTEASE LINKED TO THE ADJACENT GAG POLYPROTEIN IS ENZYMATICALLY ACTIVE

The activity of avian sarcoma leukemia virus (ASLV) protease (PR) prio r to its release from the precursor protein was determined by introduc ing mutations at the cleavage site between PR and the adjacent upstrea m nucleocapsid (No) protein. Gag DNA fragments containing these mutati ons were cloned into expression vectors and introduced into Escherichi a coil in which the ASLV proteins were expressed. The dipeptide NC-PR containing these mutations did not undergo autoprocessing when express ed in bacterial cells and the fused proteins were devoid of enzymatic activity. However, when the whole Gag polyprotein containing these mut ations was expressed in bacterial cells, other PR cleavage sites in th e viral Gag polyprotein underwent normal cleavage, indicating that the release of free PR is not a prerequisite for correct processing of th e ASLV Gag precursor. (C) 1995 Academic Press, Inc.