Topo II on the move?

The world of topoisomerase II (topo II) is changing. Until now, topo II has been thought to be a major structural protein. But on page 31, Christensen et al. show that this is an unlikely possibility. Then, in another shot to the field, they demonstrate that the two isoforms of mammalian topo II (IIα and IIβ), argued to be functionally redundant, probably make different contributions during mitosis.

Topo II passes DNA strands through each other during DNA replication and separation of sister chromatids during mitosis. It has also been considered the major nonhistone component of the mitotic chromosome scaffold. In vivo evidence to support or refute the latter role has been lacking, in part because it has been tricky to localize mammalian topo II. For example, topo IIβ has been...