SCII - AN ABUNDANT CHROMOSOME SCAFFOLD PROTEIN IS A MEMBER OF A FAMILY OF PUTATIVE ATPASES WITH AN UNUSUAL PREDICTED TERTIARY STRUCTURE

Here, we describe the cloning and characterization of ScII, the second most abundant protein after topoisomerase II, of the chromosome scaff old fraction to be identified. ScII is structurally related to a prote in, Smc1p, previously found to be required for accurate chromosome seg regation in Saccharomyces cerevisiae. ScII and the other members of th e emerging family of SMC1-like proteins are likely to be novel ATPases , with NTP-binding A and B sites separated by two lengthy regions pred icted to form an alpha-helical coiled-coil. Analysis of the ScII B sit e predicted that ScII might use ATP by a mechanism similar to the bact erial recN DNA repair and recombination enzyme. ScII is a mitosis-spec ific scaffold protein that colocalizes with topoisomerase LT in mitoti c chromosomes. However, ScII appears not to be associated with the int erphase nuclear matrix. ScII might thus play a role in mitotic process es such as chromosome condensation or sister chromatid disjunction, bo th of which have been previously shown to involve topoisomerase II.