Distribution of CENP-B boxes reflected in CREST centromere antigenic sites on long-range α-satellite DNA arrays of human chromosome 21

Abstract

The long-range organization of alphold DNA arrays of human chromosome 21 was investigated using a mouse - human somatic cell hybrid. Two distinct long alphoid DNA arrays, the loci α21-l and α21-ll, were Identified In the centromere region of human chromosome 21. The α21-l locus, composed of an array of 11 monomer repeat units (the 11 mer), was estimated to have a total length of 1.3 Mbp. CENP-B boxes, the binding sites of the centromere protein B (CENP-B), appeared In every other monomer unit in the 11 mer except for one place where two monomer units were repeated without any CENP-B box. The other locus, α21-ll, was found to be composed of alphoid subfamilies with low homology to the components of α21-l locus. Five different alphoid clones presenting 32 monomer units In total were isolated from the α21-ll locus. Sequences of these monomer units diverged between 71 – 89% and no unit containing a CENP-B box was found. By analysis using two color FISH, the α21-l was localized to the primary constriction, whereas the α21-ll site was located slightly to the short arm side. Furthermore, a combination of FISH and immuno-fluorescent staining indicated that the α21-l site was co-localized and overlapped with the CREST centromere antigenic site on mitotic chromosomes and In interphase nuclei, while a21-ll was distributed broadly. Our data suggest that the locus a21-l containing regularly spaced CENP-B boxes at high-frequency and the assembly site of the centromere antigens may be involved in common centromere function in both human and mouse cells.