Fission yeast condensin complex: essential roles of non-SMC subunits for condensation and Cdc2 phosphorylation of Cut3/SMC4

The condensin complex in frog extracts, containing two SMC (structural main tenance of chromosomes) and three non-SMC subunits, promotes mitotic chromo some condensation, and its supercoiling activity increases during mitosis b y Cdc2 phosphorylation. Here, we report that fission yeast has the same fiv e-member condensin complex, each of which is essential for mitotic condensa tion. The condensin complex was purified and the subunits were identified b y microsequencing. Cnd1, Cnd2, and Cnd3, three non-SMC subunits showing a h igh degree of sequence conservation to frog subunits, are essential for via bility, and their gene disruption leads to a phenotype indistinguishable fr om that observed in cut3-477 and cut14-208, known mutations in SMC4 and SMC 2-like subunits. Condensin subunits tagged with GFP were observed to alter dramatically their localization during the cell cycle, enriched in the nucl eus during mitosis, but cytoplasmic during other stages. This stage-specifi c alteration in localization requires mitosis-specific phosphorylation of t he T19 Cdc2 site in Cut3. The T19 site is phosphorylated in vitro by Cdc2 k inase and shows the maximal phosphorylation in metaphase in vivo. Its alani ne substitution mutant fails to suppress the temperature-sensitive phenotyp e 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.