TFG was discovered as a fusion partner of NTRK1 in human papillary thyroid carcinoma. We assembled the mouse TFG cDNA from EST sequences and 5' end RACE product, identified full coding length TFG EST clones in pig (c17b07) and Schistosoma mansoni (SMNAS62), and analyzed the genomic structure of TFG in Caenorhabditis elegans (Y63D3A). The protein sequences of mouse, pig, and S. mansoni TFG are highly homologous to human TFG. The C. elegans sequence has diverged, but its predicted secondary structure is remarkably conserved. Human, mouse, and C. elegans TFG contain a putative trimeric N-terminal coiled-coil domain, glycosylation, myristylation, and phosphorylation sites, and SH2- and SH3-binding motifs. The SH2-binding motif is absent in C. elegans TFG. The expression of TFG does not vary among 7, 11, 15, and 19 day mouse embryonal stages. In situ hybridization with a TFG probe in 10, 5-day whole mouse embryos showed preferential staining of the limb buds, branchial arches, nasal processes, and brain, and weak staining of the primitive spinal cord and dorsal root ganglia.