title: Mutational analysis of adeno-associated virus type 2 Rep68 protein endonuclease activity on partially single-stranded substrates.
abstract: The endonuclease activity of the Rep68 and Rep78 proteins (Rep68/78) of adeno-associated virus type 2 (AAV) cuts at the terminal resolution site (trs) within the hairpin structure formed by the AAV inverted terminal repeats. Recent studies suggest that a DNA unwinding function of Rep68/78 may be required for endonuclease activity. We demonstrate that several mutant proteins which are endonuclease negative on a fully duplex hairpin substrate are endonuclease positive on a partially single-stranded hairpin substrate. Truncation analysis revealed that the endonuclease function is contained within the first 200 amino acids of Rep68/78. This endonucleolytic cleavage is believed to involve the covalent attachment of Rep68/78 to the trs via a phosphate-tyrosine linkage. A previous report (S. L. Walker, R. S. Wonderling, and R. A. Owens, J. Virol. 71:2722-2730, 1997) suggested that tyrosine 152 was part of the active site. We individually mutated each tyrosine within the first 200 amino acids of the Rep68 moiety of a maltose binding protein-Rep68/78 fusion protein to phenylalanine. Only mutation of tyrosine 156 resulted in a protein incapable of covalent attachment to a partially single-stranded hairpin substrate, suggesting that tyrosine 156 is part of the endonuclease active site.
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: Davis
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: R A
authors.initials: RA
authors.lastname: Owens
mesh_terms: D001483:Base Sequence; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004279:DNA, Viral; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000229:Dependovirus / Q000201:enzymology* / Q000235:genetics; D004720:Endonucleases / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010649:Phenylalanine / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D014443:Tyrosine / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; C068734:rep proteins, Adeno-associated virus 2; D014443:Tyrosine; D010649:Phenylalanine; D004720:Endonucleases; D004265:DNA Helicases