PROCESSING AND MAJOR HISTOCOMPATIBILITY COMPLEX BINDING OF THE MTV7 SUPERANTIGEN

Mouse mammary tumor viruses produce superantigens (vSAGs) which intera ct with class II major histocompatibility complex (MHC) proteins and s timulate T cells. vSAGs are synthesized as Type II membrane proteins, but at least one of these proteins (VSAG7) is found on the cell surfac e in a proteolytically processed form. Monoclonal antibodies (MAbs) we re used to characterize VSAG7 and its binding to class II molecules. v SAG7 is synthesized in the endoplasmic reticulum (ER) as a 45 kd glyco protein containing N-asparagine-linked oligomannosyl carbohydrates. vS AG7 transits the golgi complex, where it is modified by the addition o f complex-type glycans and proteolysed at three positions. After prote olysis, the amino and carboxyl termini remain noncovalently associated . The ER, golgi, and surface forms of vSAG7 are stably bound to class II, but one of the proteolysed forms comprises the majority of the cla ss II-bound material.