Complex regulation and nuclear localization of JRK protein

The mouse jerky gene and its human orthologue, JRK/JH8, encode a putative DNA-binding protein with homology to the CENP-B (centromere-binding protein B). Disruption of the mouse jerky gene by transgene insertion causes generalized recurrent seizures reminiscent of human idiopathic generalized epilepsy. In addition (and similar to a cenp-b null mouse) jerky null mice exhibit postnatal weight loss and reduced fertility. Using fluorescence confocal microscopy, the cellular localization of a JRK–GFP fusion (where GFP stands for green fluorescent protein) was investigated in HeLa cells. JRK–GFP has a dynamic expression pattern in the interphase nucleus, localizing in a small number of punctate nuclear foci and in the nucleolus. The JRK–GFP foci number changes during the cell cycle, but a distinct pattern of three JRK–GFP foci is observed at G₂. The endogenous protein behaves in a similar manner to the GFP-fusion protein. JRK–GFP was found to co-localize with CREST antigens (which recognize the centromere-binding proteins, CENP-A, -B and -C) through S and G₂ phases of interphase and co-localized completely with a subset of PML nuclear bodies at G₂. We speculate that JRK protein associates with a specific chromosomal centromeric locus in G₂, where it associates fully with PML bodies. Research is underway to identify this locus.