Basonuclins 1 and 2, whose genes share a common origin, are proteins with widely different properties and functions

Basonuclin (bn) 1 possesses three separated pairs of zinc fingers and a nuclear localization signal. It is largely confined to the basal cells of stratified squamous epithelia and to reproductive germ cells. bn1 can shuttle between the nucleus and the cytoplasm, and its location is correlated with the proliferative potential of the cell. The recently discovered bn2 also possesses three separated pairs of zinc fingers and a nuclear localization signal. Conservation of the zinc fingers and the nuclear localization signal by bn1 and bn2 indicates a common origin. However, in contrast to bnl, bn2 is found in virtually every cell type and is confined to the nucleus. Bn2 but not bnl colocalizes with SC35 in nuclear speckles and, therefore, is likely to have a function in nuclear processing of mRNA.