Nitrogen catabolite repression transcriptional regulator; inhibits GLN3 transcription in good nitrogen source; role in sequestering Gln3p and Gat1p to the cytoplasm; has glutathione peroxidase activity and can mutate to acquire GST activity; catabolite repression normally induced by limiting nitrogen does not occur if Ure2p has polymerized to form the [URE3] prion