The function of CreA, the carbon catabolite repressor of <i>Aspergillus nidulans</i>, is regulated at the transcriptional and post‐transcriptional level

<jats:p>The <jats:italic>creA</jats:italic> gene of <jats:italic>A. nidulans</jats:italic> encodes a wide‐domain regulatory protein mediating carbon catabolite repression. Northern blot analysis of <jats:italic>creA</jats:italic> mRNA revealed a complex expression profile: the addition of monosaccharides to a carbon‐starved culture of <jats:italic>A. nidulans</jats:italic> provoked a strong transient stimulation of <jats:italic>creA</jats:italic> transcript formation within a few minutes. In the case of repressing carbon sources, <jats:italic>creA</jats:italic> mRNA levels were subsequently downregulated, whereas the high <jats:italic>creA</jats:italic> mRNA levels were maintained in a <jats:italic>creA</jats:italic> mutant strain and in the presence of derepressing monosaccharides. A high <jats:italic>creA</jats:italic> transcript level is essential to achieve carbon catabolite repression and is dependent on glucose transport and, at least partially, on the <jats:italic>creB</jats:italic> gene product. Subsequent downregulation of <jats:italic>creA</jats:italic> mRNA levels, on the other hand, is typical of carbon catabolite repression and requires a functional CreA recognition site in the <jats:italic>creA</jats:italic> promoter (and thus involves autoregulation) and formation of glucose‐6‐phosphate. Despite the presence of continuing high transcript levels of <jats:italic>creA</jats:italic> in the presence of derepressing carbohydrates, EMSA demonstrated the presence of only low levels of a CreA–DNA complex in respective cell‐free extracts. Upon transfer of carbon catabolite derepressed mycelia to catabolite‐repressing conditions, a CreA–DNA complex is formed, and this process is dependent on <jats:italic>de novo</jats:italic> protein synthesis.</jats:p>