Sister chromatid intertwines (SCIs), or catenanes, are
topological links between replicated chromatids that
interfere with chromosome segregation. The forma-
tion of SCIs is thought to be a consequence of fork
swiveling during DNA replication, and their removal
is thought to occur because of the intrinsic feature
of type II topoisomerases (Top2) to simplify DNA
topology. Here, we report that SCIs are also formed
independently of DNA replication during G
2
/M by
Top2-dependent concatenation of cohesed chroma-
tids due to their physical proximity. We demonstrate
that, in contrast to G
2
/M, Top2 removes SCIs from co-
hesedchromatidsattheanaphaseonset.Importantly,
SCI removal in anaphase requires condensin and co-
incides with the hyperactivation of condensin DNA
supercoiling activity. This is consistent with the long-
standing proposal that condensin provides a bias in
Top2functiontowarddecatenation.Acomprehensive
model for the formation and resolution of toxic SCI
entanglements on eukaryotic genomes is proposed.