T-STAR/ETOILE: a novel relative of SAM68 that interacts with an RNA-binding protein implicated in spermatogenesis

RBM is an RNA-binding protein encoded on the Y chromosome in mammals and is expressed only in the nuclei of male germ cells, Genetic evidence from inf ertile men implicates it in spermatogenesis, but its function is unknown, O f a number of potential partners for RBM identified by a yeast two-hybrid s creen with testis cDNA, the most frequent isolates encoded a novel RNA-bind ing protein, termed T-STAR, that is closely related to SAM68, an Src-associ ated protein of unknown function, The mouse homologue was also cloned and d esignated etoile, It mapped to chromosome 15, while T-STAR mapped to the sy ntenic region on human chromosome 8, T-STAR/etoile is expressed primarily i n the testis; in rat germ cells, the expression of both T-STAR/etoile and S AM68 is regulated during meiosis. Transfection of T-STAR/etoile fused with green fluorescent protein into HeLa cells caused an accumulation of protein in a novel compartment of the nucleus, adjacent to the nucleolus but disti nct from the peri-nucleolar compartment. RBM and other hnRNP G family membe rs are candidate downstream targets for regulation by T-STAR/ETOILE and SAM 68.