Phosphoribosyl Pyrophosphate Amidotransferase (PPAT)

Amidophosphoribosyltransferase is an enzyme that converts phosphoribosylpyrophosphate (PRPP) into 5-phosphoribosylamine. The enzyme uses the ammonia group from the glutamine side-chain. This is the committing step in de novo purine synthesis.

Avian GPAT and AIRC were found to be divergently transcribed from a bidirectional promoter with distinct transcriptional start sites 229 bp apart. This was said to be the first example of bidirectional transcription of tightly linked genes that are not structurally related but are involved in the same pathway. The term dioskourion was suggested to describe this eukaryotic transcriptional unit, which could be the eukaryotic equivalent of a prokaryotic operon.