Centromeres, CENP-B and Tigger too

The highly conserved centromere-associated protein CENP-B is a common feature of mammalian centromeres. Binding sites for CENP-B, so-called 'CENP-B boxes', are present in the otherwise unrelated centromeric satellite DNAs of humans, Mus musculus, Mus caroli, ferrets, giant pandas, tree shrews and gerbils, suggesting a role for CENP-B in centromere function. However, CENP-B and its binding sites are not detected at the centromeres of mammalian Y chromosomes and few, if any, binding sites seem present on African green monkey chromosomes. There is extensive sequence similarity between CENP-B and transposase proteins encoded by the pogo superfamily of transposable elements, which includes the human Tigger elements. Intriguingly, Tigger 2 has an almost perfect match to the CENP-B-binding site within its terminal inverted repeat. Comparison of the amino acid sequence of CENP-B with related proteins raises the possibility that CENP-B might share the ability to cause single-stranded DNA breaks. Such nicks could promote recombination, as has been suggested for the Charcot-Marie-Tooth disease duplication where a recombination hotspot exists close to a mariner-like element. We suggest that by promoting nicks adjacent to CENP-B boxes, CENP-B might facilitate the evolution and maintenance of satellite sequence arrays, rather than have a direct role in centromere function.