DNA‐binding proteins for transcription enhancing region of HLA class I gene

Abstract

Abstract: Class I regulatory complex (CRC) located in the 5′‐upstream region of MHC class I gene contains transcriptional enhancing sequences, called Enh A. This Enh A region contains tandem‐arranged κB‐like sites, one of which has a well‐conserved perfect palindromic sequence. The second κB‐like site, juxtaposed to the perfect palindrome, contains an imperfect palindromic sequence. In B‐cell nuclear extracts, we have identified at least four sequence‐specific protein complexes; three shared the repeated κB enhancer as their binding motifs. The perfect palindromic sequence facilitates the binding of a complex termed BI, while the imperfect palindrome provides the binding sites for two other complexes, BII and BIII. The BII and BIII complexes exhibited binding crossreactivity with other κB‐related motifs and recognized both the perfect and imperfect palindromic sequences, whereas the BI complex was specific for the perfect palindromic sequence which is unique to the class I promoters. A DNA segment outside the repeated κB enhancers probably binds the fourth complex, BIV. These complexes, except for the perfect palindrome‐binding complex, differ from those described for the murine class I promoter. The binding characteristics of these factors suggest that the mechanism controlling the class I transcription may be quite complex.