A TANDEM ARRAY OF SP-1 SITES AND A REVERSE INITIATOR ELEMENT ARE BOTHREQUIRED FOR SYNERGISTIC TRANSCRIPTIONAL ACTIVATION OF THE T-CELL-SPECIFIC MAL GENE

We have characterized the three cis elements responsible for promoter strength present in the 5'-flanking proximal region of MAL, a human T- cell-specific gene encoding a proteolipid protein present in detergent -insoluble complexes of high molecular weight. The first element consi sted of an initiator sequence that, curiously, was present in reverse orientation compared to that of the standard initiator elements, The o ther two elements were contained in a region of 126 bp upstream of the mRNA initiation site, and consisted of a tandem array of one GC box a nd one GA box. The GC box corresponds to a consensus site for the nucl ear factor Sp1, whereas the GA box deviates from this consensus, altho ugh it was able to compete for the binding of Sp1 in vitro and to resp ond to trans-activation by Sp1 in vivo. This simple promoter lacks an apparent TATA box and lost more than 99% of its activity when a fragme nt of 60 bp containing the GC and GA boxes was deleted, A synergistic effect on transcriptional activation was observed in the presence, but not in the absence, of the initiator element when both GC and GA boxe s were present.