CENP-B BINDS A NOVEL CENTROMERIC SEQUENCE IN THE ASIAN MOUSE MUS CAROLI

Minor satellite DNA, found at Mus musculus centromeres, is not present in the genome of the Asian mouse Mus caroli. This repetitive sequence family is speculated to have a role in centromere function by providi ng an array of binding sites for the centromere associated protein CEN P-B. The apparent absence of CENP-B binding sites in the M. caroli gen ome poses a major challenge to this hypothesis. Here we describe two a bundant satellite DNA sequences present at M. caroli centromeres. Thes e satellites are organized as tandem repeat arrays, over 1 Mb in size, of either 60- or 79-bp monomers. All autosomes carry both satellites and small amounts of a sequence related to the M. musculus major satel lite. The Y chromosome contains small amounts of both major satellite and the 60-bp satellite, whereas the X chromosome carries only major s atellite sequences. M. caroli chromosomes segregate in M. caroli x M. musculus interspecific hybrid cell lines, indicating that the two sets of chromosomes can interact with the same mitotic spindle. Using a po lyclonal CENP-B antiserum, we demonstrate that M. caroli centromeres c an bind murine CENP-B in such an interspecific cell line, despite the absence of canonical 17-bp CENP-B binding sites in the M. caroli genom e. Sequence analysis of the 79-bp M. caroli satellite reveals a 17-bp motif that contains all nine bases previously shown to be necessary fo r in vitro binding of CENP-B. This M. caroli motif binds CENP-B from H eLa cell nuclear extract in vitro, as indicated by gel mobility shift analysis. We therefore suggest that this motif also causes CENP-B to a ssociate with M. caroli centromeres in vivo. Despite the sequence diff erences, M. caroli presents a third, novel mammalian centromeric seque nce producing an array of binding sites for CENP-B.