DROSOPHILA PAIRED REGULATES LATE EVEN-SKIPPED EXPRESSION THROUGH A COMPOSITE BINDING-SITE FOR THE PAIRED DOMAIN AND THE HOMEODOMAIN

The even-skipped (eve) pair-rule gene plays a key role in the establis hment of the anterior-posterior segmental pattern of the Drosophila em bryo, The continuously changing pattern of eve expression can be resol ved into two phases, Early expression consists of seven broad stripes in the blastoderm embryo, while late expression, which occurs after ce llularization, consists of narrow stripes with sharp anterior borders that coincide with the odd-numbered parasegment boundaries, Previous s tudies have shown that these two phases are controlled by separate cla sses of cis elements in the eve promoter, Early stripes are expressed by multiple stripe-specific elements under the control of maternal-eff ect genes and gap genes, while late stripes are expressed by a single regulatory element, the 'late element', under the control of pair-rule genes including eve itself, We report here that paired (prd), a pair- rule gene which had been considered to be below eve in the regulatory hierarchy of pair-rule genes, in fact plays a critical role in the reg ulation of late eve expression, Transgenic analysis shows that this re gulation is largely mediated by an evolutionarily conserved sequence w ithin the late element termed PTE (Paired Target Element), In vitro an alysis shows that the Prd protein binds strongly to this sequence. Int erestingly, PTE contains juxtaposed binding sites for the two DNA-bind ing domains of the Prd protein, the paired domain and the homeodomain. Mutagenesis of either binding site leads to significant reduction in the activity of the late element, indicating that both DNA-binding dom ains in the Paired protein are required for regulation.