Mutational analysis of the DRA promoter: cis-acting sequences and trans-acting factors.

Class II major histocompatibility genes are expressed at high levels in B lymphocytes and are gamma interferon (IFN-gamma) inducible in many other cells. Previously, we observed that DRA promoter sequences from positions -150 to +31 determine the tissue specificity of this class II gene. Moreover, Z and X boxes located between positions -145 and -87 conferred B-cell specificity and IFN-gamma inducibility upon a heterologous promoter. In this study, sequences from positions -145 to -35 in the DRA promoter were systematically mutated by using oligonucleotide cassettes. Z (-131 to -125), pyrimidine (-116 to -109), X (-108 to -95), Y (-73 to -61), and octamer (-52 to -45) boxes were required for B-cell specificity and, with the exception of the octamer box, for IFN-gamma inducibility. Z box and sequences flanking Z and X boxes helped to determine low levels of expression in T and uninduced cells. In phenotypically distinct cells, shared and distinct proteins bound to these conserved upstream sequences. However, few correlations between expression and DNA-binding proteins could be made. Similar proteins bound to Z and X boxes, and the Z box most likely represents a duplication of the X box.