Identification of domains responsible for signal recognition and transduction within the QUTR transcription repressor protein

QUTR (qutR-encoded transcription-repressing protein) is a multi-domain repr essor protein active in the signal-transduction pathway that regulates tran scription of the quinic acid utilization (qut) gene cluster in Aspergillus nidulans, In the presence of quinate, production of mRNA from the eight gen es of the gut pathway is stimulated by the activator protein QUTA (qutA-enc oded transcription-activating protein). Mutations in the qutR gene after QU TR function such that the transcription of the gut gene cluster is permanen tly on (constitutive phenotype) or is insensitive to the presence of quinat e (super-repressed phenotype). These mutant phenotypes imply that the QUTR protein plays a key role in signal recognition and transduction, and we hav e used deletion analysis to determine which regions of the QUTR protein are involved in these functions. We show that the QUTR protein recognizes and binds to the QUTA protein in vitro and that the N-terminal 88 amino acids o f QUTR an sufficient to inactivate QUTA function in vivo. Deletion analysis and domain-swap experiments imply that the two C-terminal domains of QUTR are mainly involved in signal recognition.