SHARED PROMOTER ELEMENTS BETWEEN A VIRAL SUPERANTIGEN AND THE MAJOR HISTOCOMPATIBILITY COMPLEX CLASS II-ASSOCIATED INVARIANT CHAIN

Superantigens have the ability to stimulate subsets of T lymphocytes b earing particular T-cell receptor V beta chains. The best-known viral superantigen is Mls, a product of the murine mammary tumor virus (MMTV ) sag gene, The MMTV superantigen is not displayed by the virus itself ; however, after infection of B lymphocytes, the superantigen is expre ssed. The resulting immune stimulation is essential for viral transmis sion, We have analyzed the transcriptional elements which control Mls- 1 expression. Here we present evidence that a region at the 3' end of Mtv-7 env, Penv2, controls B-cell-specific expression of sag. Penv2 ha s elements homologous with promoters of immunoglobulin H chain, the in variant chain, and major histocompatibility complex class II, suggesti ng a coordinate regulation of expression of these various B-cell-speci fic genes and indicating a possible eukaryotic origin of MMTV sag. We have determined that both an IgH heptamer element and a Y box are esse ntial for Penv2 promoter activity and that tandem octamer motifs in th e U3 region of the 3' MMTV long terminal repeat function as enhancers, We propose that Penv2 controls constitutive Mls expression in B lymph ocytes.