DOMAIN-STRUCTURE AND FUNCTION WITHIN THE QUTA PROTEIN OF ASPERGILLUS-NIDULANS - IMPLICATIONS FOR THE CONTROL OF TRANSCRIPTION

QUTA is a positively acting regulatory protein that regulates the expr ession of the eight genes comprising the quinic utilization gene (qut) gene cluster in Aspergillus nidulans. It has been proposed that the Q UTA protein is composed of two domains that are related to the N-termi nal two domains dehydroquinate (DHQ) synthase and 5-enolpyruvyl shikim ate-3-phosphate (EPSP) synthase - of the pentadomain AROM protein. The AROM protein is an enzyme catalysing five consecutive steps in the sh ikimate pathway, two of which are common to the qut pathway. A genetic and molecular analysis of non-inducible qutA mutants showed that all 23 mutations analysed map within the N-terminal half of the encoded QU TA protein. One dominant mutation (qutA382) introduces a stop codon at the boundary between the two domains that were identified on the basi s of amino acid sequence alignments between the QUTA protein and the N -terminal two domains of the pentafunctional AROM protein. The truncat ed protein encoded by mutant qutA382 has DNA-binding ability but no tr anscription activation function. A second dominant mutation (in strain qutA214) is missense, changing 457E --> K in a region of localized hi gh negative charge and potentially identifies a transcription activati on domain in the N-terminus of the EPSP-synthase-like domain of the QU TA protein. A series of qualitative and quantitative Northern blot exp eriments with mRNA derived from wild-type and mutant qutA strains supp orted the view that the QUTA protein regulates the expression of the g ut gene cluster, including the qutA gene which encodes it. A series of Western blot and zinc-binding experiments demonstrated that a putativ e zinc binuclear cluster motif located within the N-terminus of the QU TA protein is able to bind zinc in vitro.