The cenpB gene is not essential in mice

Centromere protein B (CENP-B) is a centromeric DNA-binding protein that bin ds to ct-satellite DNA at the 17 bp CENP-B box sequence. The binding of CEN P-B, along with other proteins, to ct-satellite DNA sequences at the centro mere, is thought to package the DNA into heterochromatin subjacent to the k inetochore of mitotic chromosomes. To determine the importance of CENP-B to kinetochore assembly and function, we generated a mouse null for the cenpB gene. The deletion removed part of the promoter and the entire coding sequ ence except for the carboxyl-terminal 35 amino acids of the CENP-B polypept ide. Mice heterozygous or homozygous for the cenpB null mutation are viable and healthy, with no apparent defect in growth and morphology. We have est ablished mouse embryo fibroblasts from heterozygous and homozygous cenpB nu ll littermates. Microscopic analysis, using immunofluorescence and electron microscopy of the cultured cells, indicated that the centromere-kinetochor e complex was intact and identical to control cells. Mitosis was identical in fibroblasts derived from cenpB wild-type, heterozygous and null animals. Our studies demonstrate that CENP-B is not required for the assembly of he terochromatin or the kinetochore, or for completion of mitosis.