RABL ORIENTATION OF CENP-B BOX SEQUENCES IN TUPAIA-BELANGERI FIBROBLASTS

The chromosomes of the tree shrew Tupaia belangeri exhibit highly loca lized CENP-B box sequences in the centromeric regions of most chromoso mes. Telomeric sequences are present at the ends of all chromosomes an d, in addition, at specific interstitial chromosomal sites that likely represent remnants of ancestral telomeres. This suggests that Roberts onian and tandem chromosome fusion events have occurred in the karyoty pic evolution of Tupaiidae. In Tupaia skin fibroblasts CENP-B boxes ar e almost always clustered together at one pole of the interphase nucle us, whereas the telomeric domains are relatively evenly distributed th roughout the whole nuclear volume. The observed orientation of the cen tromeres is reminiscent of the Rab1 polarization of chromosomes; this is the first mammalian cell substrate in which such an higher-order ch romosomal organization has been observed. CENP-B box sequences are fou nd in several other mammalian species. The implications for recent par allel evolution of CENP-B binding motifs and concerted evolution of th ese sequences are discussed.