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J. Virol., 09 1996, 5791-5798, Vol 70, No. 9
Q Yu and JL Darlix
Nucleocapsid protein NCp10 of murine leukemia virus (MuLV) is encoded by
the 3' domain of gag and contains a zinc finger of the form Cys-X2-
Cys-X4-His-X4-Cys flanked by basic amino acids. In the course of virus
assembly, NCp10 is necessary for core formation, and the zinc finger
flanked by the basic residues is required for the packaging of the genomic
RNA dimer. In vitro, NCp10 exhibits strong nucleic acid binding and
annealing activities that appear to be critical for virus infectivity since
NCp10 promotes dimerization of the viral RNA containing the E/DLS
packaging-dimerization signal and annealing of replication primer tRNA(Pro)
to the initiation site of reverse transcription (PBS). Recent in vitro
studies have suggested that NCp10 may also play a role in proviral DNA
synthesis. To investigate the function of NCp10 in proviral DNA synthesis
in vivo, we developed a simple and convenient genetic packaging system
consisting of two DNA constructs expressing the packaging components
gag-pol and env of Friend MuLV and a Moloney MuLV-based lacZ vector with
either the MuLV E+ or a rat VL30 E packaging signal. This system allowed us
to examine the consequences of a set of mutations in NCp10 on a single
round of recombinant virus replication. Most mutations in the N- or
C-terminal domain of NCp10 do not significantly alter infectivity, while
those in the zinc finger drastically impair infectivity. Analysis of the
viral RNA content in virions showed that all mutations in the zinc finger
decrease but do not abolish packaging of the recombinant genome.
Interestingly enough, mutation of Y-28 to S (mutation Y28S) in the zinc
finger results in RNA packaging at a level similar to that observed upon
deletion of three prolines and three arginines in the C-terminal domain of
NCp10 (mutant delta PR3). However, mutant Y28S is noninfectious while
mutant delta PR3 is only threefold less infectious than the wild-type
virus, which prompted us to examine the role of NCp10 protein in proviral
DNA synthesis in vivo using these nucleocapsid mutants. PCR amplification
was used to analyze viral DNA synthesized in newly infected cells, and
results indicate that the Y28S zinc finger mutation impairs reverse
transcription, thus suggesting that the nucleocapsid protein zinc finger
plays a key role in proviral DNA synthesis in vivo.
Copyright © 1996, American Society for Microbiology
The zinc finger of nucleocapsid protein of Friend murine leukemia virus is critical for proviral DNA synthesis in vivo
LaboRetro, Institut National de la Sante et de la Recherche Medicale U412, Ecole Normale Superieure de Lyon, France.
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