Search

Mice possess two structural homologues of Drosophila HPl, termed M31 and M32 (Singh et al., 1991). We have previously shown that an M31-specific monoclonal antibody (MoAb), MAC 353, localises to constitutive heterochromatin (Wreggett et al., 1994). Here we report that a MoAb raised against the M32 protein (MAC 385) recognises a 22-kDa protein in murine nuclear extracts and that M32 is distributed in a finegrain “speckled” pattern within interphase nuclei. M32 is also largely excluded from the large masses of constitutive heterochromatin that are labelled by MAC 353.

We have raised a monoclonal antibody (MoAb), MAC 402, to the mouse M33 protein, a mammalian homologue of the Drosophila Polycomb protein. MAC 402 recognises a band of 59.7 kDa by Western blot analysis and gives rise to two types of staining pattern within interphase nuclei. Surprisingly, at metaphase, M33 protein is enriched within centromeric heterochromatin. This pattern is also seen for the product of the bmi-1 gene, which is a homologue of the Drosophila Polycomb-group (Pc-G) gene Posterior sex combs. We speculate as to the reasons for this relocalisation of mammalian Pc-G gene products to the centromere at metaphase and its implication for the cell-to-cell inheritance of the states of gene repression that are conferred by this highly conserved group of genes.