The T19 site is phosphorylated in vitro by Cdc2 kinase and shows the maximal phosphorylation in metaphase in vivo. The characterization of a human condensin complex purified from HeLa cell nuclear extracts is reported. Human condensin purified from asynchronous HeLa cell cultures fails to reconfigure DNA structure in vitro. When phosphorylated by purified cdc2-cyclin B, however, it gains the ability to introduce positive supercoils into DNA in the presence of ATP and topoisomerase I. Strikingly, human condensin can induce chromosome condensation when added back into a Xenopus egg extract that has been immunodepleted of endogenous condensin. Five genes encoding condensin components in Saccharomyces cerevisiae have been characterized.
All genes are essential for cell viability and encode proteins that form a complex in vivo.
Both SMC2 and SMC4 are essential for chromosome transmission in anaphase. Mitotic transmission of chromosome III carrying the rDNA translocation is impaired in smc2 and smc4 mutants. Thus, the condensin complex in S. cerevisiae has a specialized function in mitotic segregation of the rDNA locus. However, presence of such a complex has not been demonstrated in mammalian cells. CNAP1 associates with mitotic chromosomes and is homologous to Xenopus condensin component XCAP-D2, indicating the presence of a condensin complex in human cells.