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Journal of Virology, July 2001, p. 6537-6546, Vol. 75, No. 14
HIV-Drug Resistance Program, NCI-Frederick,
Frederick, Maryland 21702-1201
Received 5 February 2001/Accepted 25 April 2001
The amount of excess polymerase and RNase H activity in human
immunodeficiency virus type 1 virions was measured by using vectors
that undergo a single round of replication. Vectors containing wild-type reverse transcriptase (RT), vectors encoding the D110E mutation to inactivate polymerase, and vectors encoding mutations D443A
and E478Q to inactivate RNase H were constructed. 293 cells were
cotransfected with different proportions of plasmids encoding these
vectors to generate phenotypically mixed virions. The resulting viruses
were used to infect human osteosarcoma cells, and the relative
infectivity of the viruses was determined by measuring transduction of
the murine cell surface marker CD24, which is encoded by the vectors.
The results indicated that there is an excess of both polymerase and
RNase H activities in virions. Viral replication was reduced to 42% of
wild-type levels in virions with where half of the RT molecules were
predicted to be catalytically active but dropped to 3% of wild-type
levels when 25% of the RT molecules were active. However, reducing
RNase H activity had a lesser effect on viral replication. As expected,
based on previous work with murine leukemia virus, there was relatively
inefficient virus replication when the RNase H and polymerase
activities were encoded on separate vectors (D110E plus E478Q and D110E
plus D443A). To determine how virus replication failed when polymerase
and RNase H activities were reduced, reverse transcription
intermediates were measured in vector-infected cells by using
quantitative real-time PCR. The results indicated that using the D11OE
mutation to reduce the amount of active polymerase reduced the number
of reverse transcripts that were initiated and also reduced the amounts
of products from the late stages of reverse transcription. If the E478Q
mutation was used to reduce RNase H activity, the number of reverse
transcripts that were initiated was reduced; there was also a strong
effect on minus-strand transfer.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.14.6537-6546.2001
Replication of Phenotypically Mixed Human
Immunodeficiency Virus Type 1 Virions Containing Catalytically Active
and Catalytically Inactive Reverse Transcriptase
*
Corresponding author. Mailing address: HIV Drug
Resistance Program, NCI-Frederick, P.O. Box B, Building 539, Room 130A,
Frederick, MD 21702-1201. Phone: (301) 846-1619. Fax: (301) 846-6966. E-mail: Hughes{at}ncifcrf.gov.
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