STEREOSTRUCTURE OF REPLICATIVE DNA CATENANES FROM EUKARYOTIC CELLS

We isolated DNA catenanes that accumulate after inhibition of the majo r type-2 topoisomerase in eukaryotic organisms. Catenated plasmids wer e isolated from a Saccharomyces cerevisiae topoisomerase II temperatur e-sensitive mutant exposed to a nonpermissive temperature. The sterost ructure of the catenanes was analyzed by electron microscopy after coa ting the DNA with RecA protein. All were right-handed and belonged to the torus family. Catenanes arising among nascent SV40 DNA under hyper tonic growth conditions were analyzed by gel electrophoresis. Spacing of the electrophoretic ladder was consistent with a torus form. Furthe rmore, the supercoiling induced by catenation was positive, implying t hat the catenanes were right-handed. These results substantiate the hy pothesis that catenanes can be intermediates in the unlinking of the p arental strands during DNA replication.