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Nucleic Acids Research, 1977, Vol. 4, No. 12 4235-4248
© 1977

Articles

DNA-relaxing enzyme from Micrococcus luteus

R. Hecht and H. W. Thielmann

Deutsches Krebsforschungszentrum Institut für Biochemie, Im Neuenheimer Feld 280,6900 Heidelberg, GFR

Received September 2, 1977. A DNA-relaxing enzyme which catalyzes the conversion of superhelical DNA to a non-superhelical covalently closed form has been purified from Micrococcus luteus to near homogeneity by two chromatographic steps. The enzyme is a single polypeptide chain. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration on Sephadex G 150, the molecular weight is 115,000. The DNA-relaxing activity determined as a function of enzylile concentration follows a sigmoidal The enzyme requires Mg++ for activity. In the presence of 4.5 mM Mg++ addition of 50–250 mM KC1 yields incompletely relaxed DNA molecules (intermediates); intermediates are also observed in the absence of KC1, when the reaction is carried out at 0°C or at Mg++ concentrations exceeding 10 mM.


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