Homeostasis of interphase chromosome length is maintained by the SCF^Slimb E3 Ubiquitin ligase direct targeting of the Cap-H2 subunit of condensin II. Huy Nguyen¹, Christopher Bauer², Maureen Peterson¹, Daniel Buster⁴, Scott Daniel², Gregory Rogers^3,4, Giovanni Bosco¹. 1) Geisel School of Medicine, Dartmouth College, Hanover, NH; 2) Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ; 3) Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ; 4) Arizona Cancer Center, University of Arizona, Tucson, AZ.

   Although chromosomes are typically thought to undergo compaction in anticipation of mitotic segregation, it is not known whether interphase cells also require a chromosome compaction activity. Similarly, how or even if the length of interphase chromosomes is regulated is not known. Previous work from our lab has revealed that the condensin II complex functions to compact polyploid interphase chromosomes in drosophila nurse cells and salivary glands. Here, we used FISH (fluorescent in-situ hybridization) to investigate the relative contributions of condensin I, condensin II and other condensin interacting factors on chromosome length maintenance. We show that condensin II functions to regulate interphase chromosome length in Drosophila cultured Kc cells by providing an axial shortening activity. In addition, targeting of the condensin II subunit, Cap-H2, for proteasomal degradation by the F-box protein Slimb, leads to chromosome lengthening. These results show that interphase chromosome length is a regulated and dynamic feature of the interphase nucleus, and regulation of Cap-H2 protein levels is critical for chromosome length homeostasis.