BYPASSING ANAPHASE BY FISSION YEAST CUT9 MUTATION - REQUIREMENT OF CUT9(+) TO INITIATE ANAPHASE

A novel anaphase block phenotype was found in fission yeast temperatur e-sensitive cut9 mutants. Cells enter mitosis with chromosome condensa tion and short spindle formation, then block anaphase, but continue to progress into postanaphase events such as degradation of the spindle, reformation of the postanaphase cytoplasmic microtubule arrays, septa tion, and cytokinesis. The cut9 mutants are defective in the onset of anaphase and possibly in the restraint of postanaphase events until th e completion of anaphase. The cut9(+) gene encodes a 78-kD protein con taining the 10 34-amino acid repeats, tetra-tricopeptide repeats (TPR) , and similar to budding yeast Cdcl6. It is essential for viability, a nd the mutation sites reside in the TPR. The three genes, namely, nuc2 (+), scn1(+), and scn2(+), genetically interact with cut9(+). The nuc2 (+) and cut9(+) genes share an essential function to initiate anaphase . The cold-sensitive scn1 and scn2 mutations, defective in late anapha se, can suppress the ts phenotype of cut9.