Characterization and dynamic analysis of Arabidopsis condensin subunits, AtCAP-H and AtCAP-H2.

Condensin complexes are thought to play essential roles in mitotic chromosome assembly and segregation in eukaryotes. To date, two condensin complexes (condensin I and II) have been identified. Both complexes contain two structural maintenance of chromosome (SMC) subunits and three non-SMC subunits. In plants, little is known about the localization and function of all the condensin subunits. Here, we report the analyses on the localization of a non-SMC subunit of Arabidopsis condensin I and II, AtCAP-H, and AtCAP-H2, respectively. Our study indicated that localization of AtCAP-H and AtCAP-H2 is dynamically changed through the mitotic cell cycle using GFP-tagged AtCAP-H and AtCAP-H2 in tobacco cultured cells. They are localized at mitotic chromosomes from prometaphase to telophase. However, their localization in interphase is quite different. AtCAP-H was mainly found in the cytoplasm whereas AtCAP-H2 was mainly found in a nucleolus. It is revealed using GFP-tagged deletion mutant s of AtCAP-H that the kleisin-gamma middle domain (GM domain) is a unique domain only in AtCAP-H, responsible for chromosomal localization. We propose that the GM domain of CAP-H is essential for its chromosomal localization at mitosis and thus proper function of CAP-H. Differences in localization of AtCAP-H and AtCAP-H2 at interphase also suggest their functional differentiation.