The gene encoding topoisomerase II in yeast is unique and essential, required 
for both mitotic and meiotic proliferation. The use of temperature-sensitive 
mutants in topoisomerase II have demonstrated roles in the relaxation of 
tortional stress, reduction of recombination rates, and in the separation of 
sister chromatids after replication. In vertebrate cells, topoisomerase II was 
shown to be the most abundant component of the metaphase chromosomal scaffold, 
and has been shown to play a role in chromosome condensation in vitro. The cell 
cycle control of chromosome condensation may well require phosphorylation of 
topoisomerase II, since the enzyme is more highly phosphorylated in metaphase 
than in G1. Recent studies have identified casein kinase II as the major enzyme 
phosphorylating topoisomerase II in intact yeast cells. The target sites of CKII 
are exclusively in the C-terminal 400 amino acids of topoisomerase II, the 
region that is most divergent among the eukaryotic type II enzymes and which is 
absent in the bacterial gyrase homologues.