This family consists of several Barren protein homologues from several eukaryotic organisms. In Drosophila Barren (barr) is required for sister-chromatid segregation in mitosis. barr encodes a novel protein that is present in proliferating cells and has homologues in yeast and human. Mitotic defects in barr embryos become apparent during cycle 16, resulting in a loss of PNS and CNS neurons. Centromeres move apart at the metaphase-anaphase transition and Cyclin B is degraded, but sister chromatids remain connected, resulting in chromatin bridging. Barren protein localises to chromatin throughout mitosis. Colocalisation and biochemical experiments indicate that Barren associates with Topoisomerase II throughout mitosis and alters the activity of Topoisomerase II. It has been suggested that this association is required for proper chromosomal segregation by facilitating the decatenation of chromatids at anaphase [1]. This family forms one of the three non-structural maintenance of chromosomes (SMC) subunits of the mitotic condensation complex along with Cnd1 and Cnd3 [4].

1: Chromatid segregation at anaphase requires the barren product, a novel chromosome-associated protein that interacts with Topoisomerase II. Bhat MA, Philp AV, Glover DM, Bellen HJ; Cell 1996;87:1103-1114. PMID:8978614

2: Condensins, chromosome condensation protein complexes containing XCAP-C, XCAP-E and a Xenopus homolog of the Drosophila Barren protein. Hirano T, Kobayashi R, Hirano M; Cell 1997;89:511-521. PMID:9160743

3: Cnd2 has dual roles in mitotic condensation and interphase. Aono N, Sutani T, Tomonaga T, Mochida S, Yanagida M; Nature 2002;417:197-202. PMID:12000964

4: Chromosome condensation: packaging the genome. Uhlmann F; Curr Biol. 2001;11:R384-R387. PMID:11378401