Identification of InuR, a new Zn(II)2Cys6 transcriptional activator involved in the regulation of inulinolytic genes in Aspergillus niger

The expression of inulinolytic genes in Aspergillus niger is co-regulated and induced by inulin and sucrose. We have identified a positive acting transcription factor InuR, which is required for the induced expression of inulinolytic genes. InuR is a member of the fungal specific class of transcription factors of the Zn(II)2Cys6 type. Involvement of InuR in inulin and sucrose metabolism was suspected because of the clustering of inuR gene with sucB, which encodes an intracellular invertase with transfructosylation activity and a putative sugar transporter encoding gene (An15g00310). Deletion of the inuR gene resulted in a strain displaying a severe reduction in growth on inulin and sucrose medium. Northern analysis revealed that expression of inulinolytic and sucrolytic genes, e.g., inuE, inuA, sucA, as well as the putative sugar transporter gene (An15g00310) is dependent on InuR. Genome-wide expression analysis revealed, three additional putative sugar transporters encoding genes (An15g04060, An15g03940 and An17g01710), which were strongly induced by sucrose in an InuR dependent way. In silico analysis of the promoter sequences of strongly InuR regulated genes suggests that InuR might bind as dimer to two CGG triplets, which are separated by eight nucleotides

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

The definitive version is available at www.blackwell-synergy.comGenetic dissection of carbon catabolite repression in Aspergillus nidulans has identified two genes, creB and creC, which, when mutated, affect expression of many genes in both carbon catabolite repressing and derepressing conditions. The creB gene encodes a functional deubiquitinating enzyme and the creC gene encodes a protein that contains five WD40 repeat motifs, and a proline-rich region . These findings have allowed the in vivo molecular analysis of a cellular switch involving deubiquitination. We demonstrate that overexpression of the CreB deubiquitinating enzyme can partially compensate for a lack of the CreC WD40-repeat protein in the cell, but not vice versa and, thus, the CreB deubiquitinating enzyme acts downstream of the CreC WD40-repeat protein. We demonstrate using co-immunoprecipitation experiments that the CreB deubiquitinating enzyme and the CreC WD40-repeat protein interact in vivo in both carbon catabolite repressing and carbon catabolite derepressing conditions. Further, we show that the CreC WD40-repeat protein is required to prevent the proteolysis of the CreB deubiquitinating enzyme in the absence of carbon catabolite repression. This is the first case in which a regulatory deubiquitinating enzyme has been shown to interact with another protein that is required for the stability of the deubiquitinating enzyme.Robin A. Lockington and Joan M. Kell

The Wide-Domain Carbon Catabolite Repressor CreA Indirectly Controls Expression of the Aspergillus nidulans xlnB Gene, Encoding the Acidic Endo-β-(1,4)-Xylanase X(24)

The Aspergillus nidulans xlnB gene, which encodes the acidic endo-β-(1,4)-xylanase X(24), is expressed when xylose is present as the sole carbon source and repressed in the presence of glucose. That the mutation creA(d)30 results in considerably elevated levels of xlnB mRNA indicates a role for the wide-domain repressor CreA in the repression of xlnB promoter (xlnBp) activity. Functional analyses of xlnBp::goxC reporter constructs show that none of the four CreA consensus target sites identified in xlnBp are functional in vivo. The CreA repressor is thus likely to exert carbon catabolite repression via an indirect mechanism rather than to influence xlnB expression by acting directly on xlnB