INHIBITION OF PROTEIN-SERINE THREONINE PHOSPHATASES DIRECTLY INDUCES PREMATURE CHROMOSOME CONDENSATION IN MAMMALIAN SOMATIC-CELLS

Chromosomes usually condense during mitosis, but condensation may be u ncoupled from mitotic events under certain circumstances. This phenome non is known as premature chromosome condensation (PCC). Here we show that 100 nM okadaic acid or calyculin A can induce PCC at any time dur ing the cell cycle of several types of mammalian cells; G1-, S- and G2 -PCC were observed. Both okadaic acid and calyculin A are specific inh ibitors of type 1 and type 2A protein serine/threonine phosphatases, s uggesting that these phosphatases play a central role in regulating ch romosome condensation.