CAPTURING NOVEL MOUSE GENES ENCODING CHROMOSOMAL AND OTHER NUCLEAR PROTEINS

The burgeoning wealth of gene sequences contrasts with our ignorance o f gene function. One route to assigning function is by determining the sub-cellular location of proteins. We describe the identification of mouse genes encoding proteins that are confined to nuclear compartment s by splicing endogeneous gene sequences to a promoterless beta geo re porter, using a gene trap approach. Mouse ES (embryonic stem) cell lin es were identified that express beta geo fusions located within sub-nu clear compartments, including chromosomes, the nucleolus and foci cont aining splicing factors. The sequences of 11 trapped genes were ascert ained, and characterisation of endogenous protein distribution in two cases confirmed the validity of the approach. Three novel proteins con centrated within distinct chromosomal domains were identified, one of which appears to be a serine/threonine kinase, The sequence of a gene whose product co-localises with splicesome components suggests that th is protein may be an E3 ubiquitin-protein ligase. The majority of the other genes isolated represent novel genes. This approach is shown to be a powerful tool for identifying genes encoding novel proteins with specific subnuclear localisations and exposes our ignorance of the pro tein composition of the nucleus. Motifs in two of the isolated genes s uggest new links between cellular regulatory mechanisms (ubiquitinatio n and phosphorylation) and mRNA splicing and chromosome structure/func tion.