Molecular Characterization and Analysis of the acrB Gene of Aspergillus nidulans: A Gene Identified by Genetic Interaction As a Component of the Regulatory Network That Includes the CreB Deubiquitination Enzyme

Mutations in the acrB gene, which were originally selected through their resistance to acriflavine, also result in reduced growth on a range of sole carbon sources, including fructose, cellobiose, raffinose, and starch, and reduced utilization of (omega)-amino acids, including GABA and (beta)-alanine, as sole carbon and nitrogen sources. The acrB2 mutation suppresses the phenotypic effects of mutations in the creB gene that encodes a regulatory deubiquitinating enzyme, and in the creC gene that encodes a WD40-repeat-containing protein. Thus AcrB interacts with a regulatory network controlling carbon source utilization that involves ubiquitination and deubiquitination. The acrB gene was cloned and physically analyzed, and it encodes a novel protein that contains three putative transmembrane domains and a coiledcoil region. AcrB may play a role in the ubiquitination aspect of this regulatory network.