DIRECT EVIDENCE FOR THE ROLE OF COOH TERMINUS OF MOUSE MAMMARY-TUMOR VIRUS SUPERANTIGEN IN DETERMINING T-CELL RECEPTOR V-BETA SPECIFICITY

It has recently been shown that open reading frames in the 3' long ter minal repeats of mouse mammary tumor viruses encode superantigens. The se viral superantigens (vSAGs) stimulate most T cells expressing appro priate Vbetas almost regardless of the rest of the variable components of the T cell receptors (TCR) expressed by those cells. vSAGs produce a type II integral membrane protein with a nonessential short cytopla smic domain and a large glycosylated extracellular COOH-terminal domai n, which is predicted to interact with major histocompatibility comple x class II molecules and the TCR. The transmembrane region of vSAG als o has an internal positively charged lysine residue of unknown signifi cance. A set of chimeric and mutant vSAG genes has been used in transf ection experiments to show that only the extreme COOH-terminal portion of vSAGs determine their TCR Vbeta specificities, and to show that th e lysine residue in the transmembrane domain is not essential for the function of vSAG.