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Journal of Virology, September 1999, p. 7165-7174, Vol. 73, No. 9
ABL-Basic Research Program, NCI-Frederick
Cancer Research and Development Center, Frederick, Maryland
21702-1201
Received 11 February 1999/Accepted 14 May 1999
Retroviral particles contain two positive-strand genomic RNAs
linked together by noncovalent bonds that can be dissociated under mild
conditions. We studied genomic RNAs of wild-type and mutant avian
leukosis viruses (ALVs) in an attempt to (i) better understand the
site(s) of RNA dimerization, (ii) examine whether the primer binding
site (PBS) and tRNA primer are involved in dimerization, and (iii)
determine the structure of genomic RNA in protease-deficient
(PR
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Studies of the Genomic RNA of Leukosis Viruses:
Implications for RNA Dimerization
) mutants. We showed that extensively nicked wild-type
ALV genomic RNAs melt cooperatively. This implies a complex secondary
and/or tertiary structure for these RNAs that extends well beyond the 5' dimerization site. To investigate the role of the PBS-tRNA complex
in dimerization, we analyzed genomic RNAs from mutant viruses in which
the tRNATrp PBS had been replaced with sequences homologous
to the 3' end of six other chicken tRNAs. We found the genomic RNAs of
these viruses are dimers that dissociate at the same temperature as wild-type viral RNA, which suggests that the identity of the PBS and
the tRNA primer do not affect dimer stability. We studied two ALV
PR
mutants: one containing a large (>1.9-kb) inversion
spanning the 3' end of gag and much of pol,
rendering it deficient in PR, reverse transcriptase, and integrase, and
another with a point mutation in PR. In both of these mutant viruses,
the genomic RNA appears to be either primarily or exclusively
monomeric. These data suggest that ALV can package its RNA as monomers
that subsequently dimerize.
*
Corresponding author. Mailing address: NCI-Frederick
Cancer Research and Development Center, P.O. Box B, Bldg. 539, Frederick, MD 21702-1201. Phone: (301) 846-1619. Fax: (301) 846-6966. E-mail: hughes{at}ncifcrf.gov.
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