Sequence analysis predicted that TRIM is a 186-amino acid type III transmembrane protein containing an 8-amino acid extracellular domain, which includes a cys residue, and a 19-amino acid transmembrane region that lacks charged residues. The intracellular portion possesses 4 potential phosphorylation sites and 8 tyrosine residues, at least 3 of which may be involved in Src homology 2 (SH2)-mediated interactions with other signaling proteins. Northern blot analysis detected preferential expression of an approximately 2.0-kb TRIM transcript in thymus, with weaker expression in spleen, lymph nodes, and peripheral blood leukocytes. Western blot analysis of hematopoietic cell lines detected TRIM protein in T cell lines and, to a lesser extent, in natural killer cell lines, but not in B cell lines or in a monocytic cell line.