PROMOTER SPECIFICITY MEDIATES THE INDEPENDENT REGULATION OF NEIGHBORING GENES

Although enhancers can exert their influence over great distances, the ir effect is generally limited to a single gene. To discern the mechan ism by which this constraint can be mediated, we have studied three ne ighboring Drosophila genes: decapentaplegic (dpp), SLY1 homologous (Sl h) and out at first (oaf). Several dpp enhancers are positioned close to Slh and oaf, and yet these genes are unaffected by the dpp elements . However, when a transposon is located within the oaf gene, the dpp e nhancers activate the more distant transposon promoters while still ig noring the closer Slh and oaf start sites. To test whether this promot er specificity accounts for the regulatory autonomy normally found for the three genes, we used in vivo gene targeting to replace the oaf pr omoter with a dpp-compatible one in an otherwise normal chromosome. St rikingly, this chimeric gene is now activated by the dpp enhancers. Th us, the properties of the promoters themselves are sufficient to media te the autonomous regulation of genes in this region.