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Journal of Virology, March 2000, p. 2694-2702, Vol. 74, No. 6
Department of Microbiology and
Immunology1 and Medical Scientist
Training Program,2 University of Michigan
Medical School, Ann Arbor, Michigan 48109-0620
Received 20 August 1999/Accepted 8 December 1999
It has been assumed that RNA packaging constraints limit the size
of retroviral genomes. This notion of a retroviral "headful" was
tested by examining the ability of Moloney murine leukemia virus
genomes lengthened by 4, 8, or 11 kb to participate in a single
replication cycle. Overall, replication of these lengthened genomes was
5- to 10-fold less efficient than that of native-length genomes. When
RNA expression and virion formation, RNA packaging, and early stages of
replication were compared, long genomes were found to complete each
step less efficiently than did normal-length genomes. To test whether
short RNAs might facilitate the packaging of lengthy RNAs by
heterodimerization, some experiments involved coexpression of a short
packageable RNA. However, enhancement of neither long vector RNA
packaging nor long vector DNA synthesis was observed in the presence of
the short RNA. Most of the proviruses templated by 12 and 16 kb vectors
appeared to be full length. Most products of a 19.2-kb vector contained
deletions, but some integrated proviruses were around twice the native
genome length. These results demonstrate that lengthy retroviral
genomes can be packaged and that genome length is not strictly limited
at any individual replication step. These observations also suggest that the lengthy read-through RNAs postulated to be intermediates in
retroviral transduction can be packaged directly without further processing.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Replication of Lengthened Moloney Murine Leukemia
Virus Genomes Is Impaired at Multiple Stages
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, University of Michigan Medical School,
5641 Medical Sciences Bldg. II, Ann Arbor, MI 48109-0620. Phone: (734) 936-6466. Fax: (734) 764-3562. E-mail: ateles{at}umich.edu.
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