P93(DIS1), WHICH IS REQUIRED FOR SISTER-CHROMATID SEPARATION, IS A NOVEL MICROTUBULE AND SPINDLE POLE BODY-ASSOCIATING PROTEIN PHOSPHORYLATED AT THE CDC2 TARGET SITES

Fission yeast cold-sensitive (cs) dis1 mutants are defective in sister chromatid separation. The dis1(+) gene was isolated by chromosome walking. The null mutant showed the same phenotype as that of cs mutants. The dis1(+) gene product was identified as a novel 93-kD protein, and its localization was determined by use of anti-dis1 antibodies and green fluorescent protein (GFP) tagged to the carboxyl end of p93(dis1). The tagged p93(dis1) in living cells localizes along cytoplasmic microtubule arrays in interphase and the elongating anaphase spindle in mitosis, but association with the short metaphase spindle microtubules is strikingly reduced. In the spindle, the tagged p93(dis1) is enriched at the spindle pole bodies (SPBs). Time-lapse video images of single cells support the localization shift of p93(dis1) to the SPBs in metaphase and spindle microtubules in anaphase. The carboxy-terminal fragment, which is essential for Dis1 function, accumulates around the mitotic SPB. We propose that these localization shifts of p93(dis1) in mitosis facilitates sister chromatid separation by affecting SPB and anaphase spindle function.