The purification from Escherichia coli of a protein relaxing superhelical DNA

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Abstract
The E. coli omega protein was 1st described by Wang as having the ability to relax supercoiled covalently-closed circular DNA by changing the topological winding number, .alpha.. A rapid assay was developed for omega activity which allowed purification of the protein to homogeneity. It appears to be an .alpha..beta.-type subunit protein with a MW of the intact protein of about 80,000 (determined by gel filtration) and of the individual subunits of 56,000 and 31,000 (sodium dodecyl sulfate polyacrylamide gels). Wang''s observation that it only partly relaxes negative supercoils and is not active on positive supercoils was confirmed. Its characteristics with respect to pH, salts, temperature and chromatography are described. A method for rapid screening of E. coli for omega mutants is described.

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