HEAT repeats associated with condensins, cohesins, and other complexes involved in chromosome-related functions

HEAT repeats correspond to tandemly arranged curlicue-like structures that appear to serve as flexible scaffolding on which other components can assem ble. Using sensitive sequence analysis techniques we detected HEAT repeals in various chromosome-associated proteins, including four Families of prote ins associated with condensins and cohesins, which are nuclear complexes th at contain structural maintenance of chromosome (SMC) proteins. Among the p roteins detected were the XCAP-D2 and XCAP-G subunits of the Xenopus laevis 13S condensin complex, the Aspergillus BimD and Sordaria macrospora Spo76p proteins, the budding yeast Scc2p protein, and the related Drosophila tran scriptional activator Nipped-B. Clathrin adaptor and COP-I coatomer subunit s, which Function in vesicle coat assembly and were previously noted to sha re weak sequence similarity to condensin subunits, also contain HEAT repeat s. HEAT repeats were also found in the TBP-associated TIP120 protein, a glo bal enhancer of transcription, and in the budding yeast Motlp protein, whic h is a member of the SWI2/SNF2 family. SWI2/SNF2 proteins, some of which ar e helicases, perform diverse roles in transcription control, DNA repair, an d chromosome segregation and form chromatin-remodeling complexes. HEAT repe ats also were found in disl-TOG family and cofactor D family microtubule-as sociated proteins, which, owing to their roles in microtubule dynamics, per form functions related to mitotic progression and chromosome segregation. H ence, our analysis predicts structural Features of these proteins and sugge sts that HEAT repeats may play important roles in chromosome dynamics.