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M94B0782.TXT
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1994-11-11
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Document 0782
DOCN M94B0782
TI Analysis of strand transfer synthesis by reverse transcriptases.
DT 9412
AU Buiser RG; Univ. of Rochester
SO Diss Abstr Int [B]; 54(7):3597 1994. Unique Identifier : AIDSLINE
ICDB/94605826
AB Models of retrovirus replication require the viral reverse transcriptase
(RT) to catalyze two distinct strand transfer reactions. In this
process, an RNA primer is elongated on one template and then transferred
to another template for additional elongation. It is thought that the RT
ribonuclease H (RNase H) activity is involved in both transfer
reactions. The properties of reverse transcriptases required for strand
transfer synthesis have been examined using poly(rA) as a model
substrate. In this system, strand transfer is observed by the appearance
of products much longer than the templates used to generate them. RTs
from human immunodeficiency (HIV), avian myeloblastosis (AMV), and
murine leukemia (MuLV) viruses differ in molecular mass and subunit
composition. However, they all catalyze strand transfer synthesis on
poly(rA)300, generating characteristically long products. An RNase H
deficient enzyme, HIV-RT(RD,) catalyzed strand transfer synthesis to the
same degree as native HIV-RT, indicating that a functional RNase H
activity is not required for this process. Additionally,
N-ethylmaleimide (NEM), which inhibits RNase H but not polymerase
activity of HIV-RT, did not diminish strand transfer synthesis. Highly
processive DNA synthesis by each RT was found to be a requirement for
the strand transfer reaction. Catalysis of strand transfer synthesis is
not a property of all DNA polymerases, since the Klenow fragment of
Escherichia coli DNA polymerase I is unable to catalyze this reaction.
These results suggest that strand transfer synthesis relies on an
unidentified functional activity present in RTs. The ability of RTs to
catalyze strand transfer, or template switching, from internal regions
of RNA templates has also been examined. To study this phenomenon, a
system of donor and acceptor templates was employed in which homologous
strand transfer can occur from a homopolymeric sequence positioned
internally on the donor template. Our results indicate that HIV-, AMV-,
and MuLV-RTs are all able to catalyze strand transfer from this internal
homopolymeric sequence. Catalysis of this reaction is not dependent upon
RNase H activity, since HIV-RT(RD) is able to catalyze the reaction
efficiently. Additionally, NEM did not inhibit strand transfer by either
the native or RNase H deficient forms of HIV-RT. Our data further
indicate that template switching may be promoted by RT pausing at a
specific site on the donor template. Conditions that increase RT pausing
at this site also increase template switching. These results suggest
that transient RT pausing at specific sites on the viral genome during
reverse transcription may promote strand transfers that in turn lead to
recombination. (Full text available from University Microfilms
International, Ann Arbor, MI, as Order No. AAD93-34491)
DE DNA Polymerase I/GENETICS Ethylmaleimide/PHARMACOLOGY *Reverse
Transcriptase/*GENETICS Ribonucleases/*GENETICS THESIS
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).