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Journal of Virology, December 2001, p. 11365-11372, Vol. 75, No. 23
Departments of
Medicine1 and
Microbiology,2 University of Alabama at
Birmingham, Birmingham, Alabama 35294, and Research Service,
Birmingham Veterans Affairs Medical Center, Birmingham, Alabama
352333
Received 2 July 2001/Accepted 5 September 2001
Mutations in the IN domain of retroviral DNA
may affect multiple steps of the virus life cycle, suggesting that the
IN protein may have other functions in addition to its integration
function. We previously reported that the human immunodeficiency virus
type 1 IN protein is required for efficient viral DNA synthesis and that this function requires specific interaction with other viral components but not enzyme (integration) activity. In this report, we
characterized the structure and function of the Moloney murine leukemia
virus (MLV) IN protein in viral DNA synthesis. Using an MLV vector
containing green fluorescent protein as a sensitive reporter for virus
infection, we found that mutations in either the catalytic triad
(D184A) or the HHCC motif (H61A) reduced infectivity by approximately
1,000-fold. Mutations that deleted the entire IN (
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.23.11365-11372.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Moloney Murine Leukemia Virus Integrase Protein
Augments Viral DNA Synthesis in Infected Cells
IN) or 34 C-terminal amino acid residues (
34) were more severely defective,
with infectivity levels consistently reduced by 10,000-fold. Immunoblot
analysis indicated that these mutants were similar to wild-type MLV
with respect to virion production and proteolytic processing of the Gag
and Pol precursor proteins. Using semiquantitative PCR to analyze viral
cDNA synthesis in infected cells, we found the
34 and
IN mutants
to be markedly impaired while the D184A and H61A mutants synthesized
cDNA at levels similar to the wild type. The DNA synthesis defect was rescued by complementing the
34 and
IN mutants in
trans with either wild-type IN or the D184A mutant IN,
provided as a Gag-IN fusion protein. However, the DNA synthesis defect
of
IN mutant virions could not be complemented with the
34 IN
mutant. Taken together, these analyses strongly suggested that the MLV
IN protein itself is required for efficient viral DNA synthesis and
that this function may be conserved among other retroviruses.
*
Corresponding author. Mailing address: University of
Alabama at Birmingham, Department of Medicine, THT 513H, 1530 3rd Ave. South, Birmingham, AL 35294. Phone: (205) 934-0051. Fax: (205) 975-7300. E-mail: kappesjc{at}uab.edu.
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