Nucleic Acids Research, Vol 25, Issue 11 2091-2097, Copyright © 1997 by Oxford University Press
BO Petersen and S Shuman
Vaccinia topoisomerase forms a covalent protein-DNA intermediate at sites
containing the sequence 5'-CCCTT. The T nucleotide is linked via a
3'-phosphodiester bond to Tyr-274 of the enzyme. Here, we report that the
enzyme catalyzes hydrolysis of the covalent intermediate, resulting in
formation of a 3'-phosphate-terminated DNA cleavage product. The hydrolysis
reaction is pH-dependent (optimum pH = 9.5) and is slower, by a factor of
10(-5), than the rate of topoisomerase-catalyzed strand transfer to a 5'-OH
terminated DNA acceptor strand. Mutants of vaccinia topoisomerase
containing serine or threonine in lieu of the active site Tyr-274 form no
detectable covalent intermediate and catalyze no detectable DNA hydrolysis.
This suggests that hydrolysis occurs subsequent to formation of the
covalent protein-DNA adduct and not via direct attack by water on DNA.
Vaccinia topoisomerase also catalyzes glycerololysis of the covalent
intermediate. The rate of glycerololysis is proportional to glycerol
concentration and is optimal at pH 9.5.
ARTICLES
DNA strand transfer reactions catalyzed by vaccinia topoisomerase: hydrolysis and glycerololysis of the covalent protein-DNA intermediate
Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10021, USA.
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