A Drosophila metabolic gene transcript is alternatively processed.

We have determined the organization and transcription of a Drosophila DNA segment coding for the purine pathway enzyme, GAR transformylase. Because the transcript encoding this enzyme is very rare, we used a novel method for exon mapping without isolating a cDNA. Our results suggest a long polypeptide having multiple domains, with GAR transformylase at the COOH terminus preceded by an extensive repeat. Part of the same DNA segment specifies a shorter transcript, which consists of the same 5' exons but lacks the last three 3' exons. A polyadenylation signal within an intron allows this single gene to encode two polypeptides. We hypothesize that alternative processing of a transcript is a basis for channeling metabolic intermediates into two different pathways.