COEXPRESSION OF 2 CLOSELY LINKED AVIAN GENES FOR PURINE NUCLEOTIDE SYNTHESIS FROM A BIDIRECTIONAL PROMOTER

Two avian genes encoding essential steps in the purine nucleotide bios ynthetic pathway are transcribed divergently from a bidirectional prom oter element. The bidirectional promoter, embedded in a CpG island, di rects coexpression of GPAT and AIRC genes from distinct transcriptiona l start sites 229 bp apart. The bidirectional promoter can be divided in half, with each half retaining partial activity towards the cognate gene. GPAT and AIRC genes encode the enzymes that catalyze step 1 and steps 6 plus 7, respectively, in the de novo purine biosynthetic path way. This is the first report of genes coding for structurally unrelat ed enzymes of the same pathway that are tightly linked and transcribed divergently from a bidirectional promoter. This arrangement has the p otential to provide for regulated coexpression comparable to that in a prokaryotic operon.