Association of mouse mammary tumor virus superantigen with MHC class II during biosynthesis

Mouse mammary tumor viruses encode superantigens that interact with MHC cla ss II proteins and stimulate T cells. We show here that presentation of mou se mammary tumor virus superantigen does not require DM. Furthermore, we ha ve identified a strong class II peptide binding motif in the Mtv-7 superant igen, and we show that this motif is necessary for association with class I I molecules in in vitro translation and in vivo functional assays. Our resu lts suggest that endogenously synthesized viral superantigen can bind to MH C class II heterodimers during biosynthesis in the endoplasmic reticulum in a manner analogous to that used by the class II-associated invariant chain .