THE INVARIANT CHAIN GENE INTRONIC ENHANCER SHOWS HOMOLOGY TO CLASS-IIPROMOTER ELEMENTS

Coordinate expression of MHC class II proteins and the class II-associ ated invariant chain (Ii) is important for proper MHC class II functio ning in Ag processing and presentation. The coordinate regulation of t hese genes results, in part, from the sharing of transcriptional regul atory regions between MHC class II and Ii genes; the Ii has previously been shown to have an upstream enhancer closely related to the essent ial class II promoter elements. We report here the characterization of a second enhancer in the Ii gene, located within the first intron, Th is intronic enhancer is contained within a 155-bp region, enhances tra nscription from the Ii minimal promoter, and also contains elements th at are homologous to class II promoter elements X1, X2, and Y boxes.