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

Abstract

QUTR (qutR-encoded transcription-repressing protein) is a multi-domain repressor protein active in the signal-transduction pathway that regulates transcription of the quinic acid utilization (qut) gene cluster in Aspergillus nidulans. In the presence of quinate, production of mRNA from the eight genes of the qut pathway is stimulated by the activator protein QUTA (qutA-encoded transcription-activating protein). Mutations in the qutR gene alter QUTR function such that the transcription of the qut gene cluster is permanently on (constitutive phenotype) or is insensitive to the presence of quinate (super-repressed phenotype). These mutant phenotypes imply that the QUTR protein plays a key role in signal recognition and transduction, and we have 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 of QUTR are 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.

The WD40‐repeat protein CreC interacts with and stabilizes the deubiquitinating enzyme CreB in vivo in Aspergillus nidulans

“…Whether this action is via the pathway‐specific regulatory proteins involved in induction, such as PrnA in the case of proline utilization (Cazelle et al , 1998), or QutR and QutA in the case of quinate utilization (Lamb et al. , 1996; Levett et al , 2000), or directly on the enzymes or permeases themselves, is not known. In the absence of CreC, no full‐length CreB protein can be seen in quinate‐grown mycelium, and only very poor utilization of quinate is seen, consistent with this model.…”