Nuclear export-dependent degradation of the carbon catabolite repressor CreA is regulated by a region located near the C-terminus in Aspergillus oryzae.

Carbon catabolite repression (CCR) is regulated by the C2 H2 -type transcription factor CreA/Cre1 in filamentous fungi including Aspergillus oryzae. We investigated the stability and subcellular localization of CreA in A. oryzae. The abundance of FLAG-tagged CreA (FLAG-CreA) was dramatically reduced after incubation in maltose and xylose, which stimulated the export of CreA from the nucleus to the cytoplasm. Mutation of a putative nuclear export signal resulted in nuclear retention and significant stabilization of CreA. These results suggest that CreA is rapidly degraded in the cytoplasm after export from the nucleus. The FLAG-CreA protein level was reduced by disruption of creB and creC, which encode the deubiquitinating enzyme complex involved in CCR. In contrast, FLAG-CreA stability was not affected by disruption of creD which encodes an arrestin-like protein required for CCR relief. Deletion of the last 40 C-terminal amino acids resulted in remarkable stabilization and increased abundance of FLAG-CreA, whereas deletion of the last 20 C-terminal amino acids had no apparent effect on CreA stability. This result suggests that the 20 amino acid region located between positions 390 and 409 of CreA is critical for the rapid degradation of CreA.