The condensin complex in frog extracts, containing two SMC (structural 
maintenance of chromosomes) and three non-SMC subunits, promotes mitotic 
chromosome condensation, and its supercoiling activity increases during mitosis 
by Cdc2 phosphorylation. Here, we report that fission yeast has the same 
five-member condensin complex, each of which is essential for mitotic 
condensation. The condensin complex was purified and the subunits were 
identified by microsequencing. Cnd1, Cnd2, and Cnd3, three non-SMC subunits 
showing a high degree of sequence conservation to frog subunits, are essential 
for viability, and their gene disruption leads to a phenotype indistinguishable 
from that observed in cut3-477 and cut14-208, known mutations in SMC4 and 
SMC2-like subunits. Condensin subunits tagged with GFP were observed to alter 
dramatically their localization during the cell cycle, enriched in the nucleus 
during mitosis, but cytoplasmic during other stages. This stage-specific 
alteration in localization requires mitosis-specific phosphorylation of the T19 
Cdc2 site in Cut3. The T19 site is phosphorylated in vitro by Cdc2 kinase and 
shows the maximal phosphorylation in metaphase in vivo. Its alanine substitution 
mutant fails to suppress the temperature-sensitive phenotype of cut3-477, and 
shows deficiency in condensation, probably because Cut3 T19A remains 
cytoplasmic. Therefore, direct Cdc2 phosphorylation of fission yeast condensin 
may facilitate its nuclear accumulation during mitosis.