Mapping the active-site tyrosine of vaccinia virus DNA topoisomerase I

S. Shuman, E. M. Kane, S. G. Morham

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Site-directed mutagenesis of the vaccinia virus gene encoding a type I DNA topoisomerase implicates Tyr-274 as the active-site residue that forms a covalent adduct with DNA during cycles of DNA-strand breakage and reunion. Replacement of Tyr-274 by phenylalanine results in loss of the ability of the enzyme to relax negatively supercoiled DNA as well as to form the covalent DNA-protein intermediate. Substitution of phenylalanine for tyrosine at nine other sites in the protein has no apparent effect on enzyme activity. Amino acid sequence alignment reveals Tyr-274 to be homologous to Tyr-727 and Tyr-771, respectively, of the type I topoisomerases from Saccharomyces cerevisiae and Saccharomyces pombe; Tyr-727 and Tyr-771 have been shown to represent the active-site tyrosines of those enzymes. Sequence comparison of the active-site regions defines a motif Ser-Lys-Xaa-Xaa-Tyr common to the viral and cellular type I topoisomerases, including the human enzyme.

Original languageEnglish (US)
Pages (from-to)9793-9797
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number24
StatePublished - 1989

All Science Journal Classification (ASJC) codes

  • General


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