POLARITY AND SPECIFIC SEQUENCE REQUIREMENTS OF PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR (PPAR) RETINOID-X-RECEPTOR HETERODIMER BINDING TODNA - A FUNCTIONAL-ANALYSIS OF THE MALIC ENZYME GENE PPAR RESPONSE ELEMENT

The malic enzyme (ME) gene is a target for both thyroid hormone recept ors and peroxisome proliferator-activated receptors (PPAR). Within the ME: promoter; two direct repeat (DR)-1-like elements, MEp and MEd, ha ve cell identified as putative PPAR response elements (PPRE), We demon strate that only MEp and not MEd is able to bind PPAR/retinoid X recep tor (RXR) heterodimers and mediate peroxisome proliferator signaling. Taking advantage of the close sequence resemblance of MEp and MEd, we have identified crucial determinants of a PPRE, Using reciprocal mutat ion analyses of these two elements, we show the preference for adenine as the spacing nucleotide between the two half-sites of the PPRE and demonstrate the importance of the two first bases flanking the core DR 1 in 5', This latter feature of the PPRE lead us to consider the polar ity of the PPAR/RXR heterodimer bound to its cognate element, We demon strate that, in contrast to the polarity of RXR/TR and RXR/RAR bound t o DR4 and DR5 elements respectively, PPAR binds to the 5' extended hal f-site of the response element, while RXR occupies the 3' half-site, C onsistent with this polarity is our finding that formation and binding of the PPAR/RXR. heterodimer requires an intact. hinge T region in RX R while its integrity is not required for binding of the RXR/TR hetero dimer to a DR4.