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Journal of Virology, October 1999, p. 8073-8082, Vol. 73, No. 10
Department of Microbiology, The University of
Alabama at Birmingham, Birmingham, Alabama 35294
Received 12 March 1999/Accepted 7 July 1999
Mason-Pfizer monkey virus (M-PMV), the prototypical type D
retrovirus, assembles immature capsids within the cytoplasm of the cell
prior to plasma membrane interaction. Several mutants of M-PMV Gag have
been described which display altered transport, assembly, or both. In
this report, we describe the use of an in vitro synthesis and assembly
system to distinguish between defects in intracellular transport and
the process of assembly itself for two previously described
gag gene mutants. Matrix domain mutant R55W converts the
type D morphogenesis of M-PMV particles into type C and has been
hypothesized to alter the transport of Gag, redirecting it to the
plasma membrane where assembly subsequently occurs. We show here that
R55W can assemble in both the in vitro translation-assembly system and
within inclusion bodies in bacteria and thus has retained the capacity
to assemble in the cytoplasm. This supports the concept that R55 is
located within a domain responsible for the transport of Gag to an
intracellular site for assembly. In contrast, deletions within the p12
domain of M-PMV Gag had previously been shown to affect the efficiency
of particle formation such that under low-level expression conditions, Gag would fail to assemble. We demonstrate here that the efficiency of
assembly in the in vitro system mirrors that seen in cells under
expression conditions similar to that of an infection. These results
argue that the p12 domain of this D-type retrovirus plays a critical
role in the membrane-independent assembly of immature capsids.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Separate Assembly and Transport Domains within the
Gag Precursor of Mason-Pfizer Monkey Virus
*
Corresponding author. Mailing address: Department of
Microbiology, The University of Alabama at Birmingham, 256 Bevill
Biomedical Research Building, 845 19th St. South, Birmingham, AL
35294-2170. Phone: (205) 934-4321. Fax: (205) 934-1640. E-mail:
ehunter{at}uab.edu.
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