title: Interaction of wild-type and mutant adeno-associated virus (AAV) Rep proteins on AAV hairpin DNA.
abstract: Both the Rep68 and Rep78 proteins of adeno-associated virus type 2 (AAV) bind to AAV terminal repeat hairpin DNA and can mediate site-specific nicking in vitro at the terminal resolution site (trs) within the terminal repeats. To define the regions of the Rep proteins required for these functions, a series of truncated Rep78 derivatives was created. Wild-type and mutant proteins were synthesized by in vitro translation and analyzed for AAV hairpin DNA binding, trs endonuclease activity, and interaction on hairpin DNA. Amino-terminal deletion mutants which lacked the first 29 or 79 amino acid residues of Rep78 did not bind hairpin DNA, which is consistent with our previous identification of a DNA-binding domain in this region. Progressive truncation of the carboxyl-terminal region of Rep78 did not eliminate hairpin DNA binding until the deletion reached amino acid 443. The electrophoretic mobility of the Rep-specific protein-DNA complexes was inversely related to the molecular weight of the Rep derivative. Analysis of the C-terminal deletion mutants by the trs endonuclease assay identified a region (amino acids 467 to 476) that is essential for nicking but is not necessary for DNA binding. When endonuclease-positive, truncated Rep proteins that bound hairpin DNA were mixed with full-length Rep78 or Rep68 protein in electrophoretic mobility shift assays, a smear of protein-DNA complexes was observed. This smear migrated at an intermediate position with respect to the bands generated by the proteins individually. An antibody recognizing only the full-length protein produced a novel supershift band when included in a mixed binding assay containing Rep68 and a truncated Rep mutant. These experiments suggest that the Rep proteins can form hetero-oligomers on the AAV hairpin DNA.
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Weitzman
authors.forename: S R
authors.initials: SR
authors.lastname: Kyöstiö
authors.forename: B J
authors.initials: BJ
authors.lastname: Carter
authors.forename: R A
authors.initials: RA
authors.lastname: Owens
mesh_terms: D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000229:Dependovirus / Q000235:genetics / Q000378:metabolism*; D004720:Endonucleases / Q000378:metabolism; D006801:Humans; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017384:Sequence Deletion; D013728:Terminator Regions, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D014764:Viral Proteins; C068734:rep proteins, Adeno-associated virus 2; D004247:DNA; D004720:Endonucleases