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Journal of Virology, April 2000, p. 3122-3129, Vol. 74, No. 7
Laboratory of Molecular Hematology, National
Heart, Lung, and Blood Institute, Bethesda, Maryland 20892
Received 23 September 1999/Accepted 10 January 2000
The Rep78 protein of adeno-associated virus (AAV) contains amino
acid sequence motifs common to rolling-circle replication (RCR)
initiator proteins. In this report, we describe RCR initiator-like activities of Rep78. We demonstrate that a maltose-binding protein (MBP)-Rep78 fusion protein can catalyze the cleavage and ligation of
single-stranded DNA substrates derived from the AAV origin of
replication. Rep-mediated single-stranded DNA cleavage was strictly
dependent on the presence of certain divalent cations (e.g.,
Mn2+ or Mg2+) but did not require the presence
of a nucleoside triphosphate cofactor. Electrophoretic mobility shift
assays demonstrated that binding of single-stranded DNA by MBP-Rep78
was influenced by the length of the substrate as well as the presence
of potential single-stranded cis-acting sequence elements.
Site-directed mutagenesis was used to examine the role of specific
tyrosine residues within a conserved RCR motif (motif 3) of Rep78.
Replacement of Tyr-156 with phenylalanine abolished the ability of
MBP-Rep78 to mediate the cleavage and ligation of single-stranded DNA
substrates but not the ability to stably bind single-stranded DNA. The
cleaving-joining activity of Rep78 is consistent with the mechanism of
replicative intermediate dimer resolution proposed for the autonomous
parvoviruses and may have implications for targeted integration of
recombinant AAV vectors.
0022-538X/00/$04.00+0
An Adeno-Associated Virus (AAV) Initiator
Protein, Rep78, Catalyzes the Cleavage and Ligation of
Single-Stranded AAV ori DNA
*
Corresponding author. Mailing address: LMH, NHLBI,
Bldg. 10, Rm. 7D18, Bethesda, MD 20892-1654. Phone: (301) 496-1594. Fax: (301) 496-9985. E-mail: kotinr{at}nhlbi.nih.gov.
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