Arch Virol (1998) 143: 381–388
Moloney murine leukemia virus protease expressed
in bacteria is enzymatically active
, G. Schumann, and J. D. Boeke
Department of Molecular Biology and Genetics, Johns Hopkins University
School of Medicine, Baltimore, Maryland, U.S.A.
Accepted September 20, 1997
Summary. Replication of Moloney murine leukemia virus requires a readthrough
translation mechanism to generate the Gag-Pol polyprotein. One of the ﬁnal prod-
ucts of this polyprotein is the protease (PR), which is required to generate the ma-
ture virion proteins. The assembly of Gag and Gag-Pol polyproteins into a virion
followed by activation of the viral protease is necessary to produce a mature,
infectious particle. These events are believed to occur near the cell membrane
just prior to the budding of the virion. We report here the autoproteolytic activity
of the viral PR when a Gag-PR fusion protein is expressed in E. coli. Efﬁcient
cleavage at the p12/CA, CA/NC and NC/PR junctions was observed. Thus the
Moloney murine leukemia virus PR is capable of cleaving its substrates in the
absence of speciﬁc host factors.
Retrovirusesintegratetheirgenome into the DNA of their host cells through a well
known but complex cascade of molecular events. In the immature virion of the
Moloney murine leukemia virus (M-MuLV) full-length viral RNA is surrounded
by a shell consisting of the polyprotein precursors Gag and Gag-Pol . These
precursor proteins are processed to the mature, functional viral proteins matrix
(MA), capsid (CA), nucleocapsid (NC), reverse transcriptase (RT), integrase (IN),
and protease (PR) during or just after viral assembly . The viral PR is essential
for replication, forming a dimer that speciﬁcally cleaves the Gag and Gag-Pol
Life Technologies, Gaithersburg, MD, U.S.A.
Gen Vec Inc.,
Rockville, MD 20852, U.S.A.