Journal of Virology, January 2001, p. 260-268, Vol. 75, No. 1
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.1.260-268.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Departments of Medicine2 and of Microbiology and Immunology,1 The Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033
Received 30 May 2000/Accepted 27 September 2000
The genomic RNA of retroviruses exists within the virion as a
noncovalently linked dimer. Previously, we identified a mutant of the
viral matrix (MA) protein of Rous sarcoma virus that disrupts viral RNA
dimerization. This mutant, Myr1E, is modified at the N terminus of MA
by the addition of 10 amino acids from the Src protein, resulting in
the production of particles containing monomeric RNA. Dimerization is
reestablished by a single amino acid substitution that abolishes
myristylation (Myr1E
). To distinguish between cis and
trans effects involving Myr1E, additional mutations were generated. In Myr1E.cc and Myr1E
.cc, different nucleotides were utilized to encode the same protein as Myr1E and Myr1E
, respectively. The alterations in RNA sequence did not change the properties of the
viral mutants. Myr1E.ATG
was constructed so that translation began at
the gag AUG, resulting in synthesis of the wild-type Gag
protein but maintenance of the src RNA sequence. This
mutant had normal infectivity and dimeric RNA, indicating that the
src sequence did not prevent dimer formation.
All of the src-containing RNA sequences formed dimers in
vitro. Examination of MA-green fluorescent protein fusion proteins
revealed that the wild-type and mutant MA proteins Myr1E.ATG
,
Myr1E
, and Myr1E
.cc had distinctly different patterns of
subcellular localization compared with Myr1E and Myr1E.cc MA proteins.
This finding suggests that proper localization of the MA protein may be
required for RNA dimer formation and infectivity. Taken together, these
results provide compelling evidence that the genomic RNA dimerization
defect is due to a trans-acting effect of the mutant MA proteins.
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