Chemical modification of essential tyrosine residues in DNA topoisomerases

Abstract

Micrococcus luteus topoisomerases I and II (DNA gyrase) are rapidly inactivated by tetranitromethane, a chemical modification reagent with a demonstrated specificity for tyrosine residues in proteins. Binding of toposiomerases to DNA prior to reaction with tetranitromethane protects essential tyrosine residues and prevents chemical inactivation of the enzymes. Recently, topoisomerase-DNA complexes have been shown to form covalent phosphate-tyrosine linkages upon treatment with protein-denaturing reagents (Tse, Y.-C., et al. (1980) J. Biol. Chem. 225, 5560–5565). In the present study we demonstrate an essential role for tyrosine in the catalytic activity of DNA topoisomerases, determined under conditions where the enzymes bind to DNA in a reversible manner.