13S condensin actively reconfigures DNA by introducing global positive writhe: Implications for chromosome condensation

Xenopus 13S condensin converts interphase chromatin into mitotic-like chrom osomes, and, in the presence of ATP and a type I topoisomerase, introduces (+) supercoils into DNA. The specific production of (+) trefoil knots in th e presence of condensin and a type II topoisomerase shows that condensin re configures DNA by introducing an ordered, global, (+) writhe. Knotting requ ired ATP hydrolysis and cell cycle-specific phosphorylation of condensin. C ondensin bound preferentially to (+) supercoiled DNA in the presence of ATP but not in its absence. Our results suggest a mechanism for the compaction of chromatin by condensin during mitosis.