The protein RrmA is involved in posttranscriptional regulation of gene expression in Aspergillus nidulans. rrmA mutations were first selected on the basis of altered arginine/proline metabolism, leading to suppression of proline auxotrophy in a proA- strain. Independently of this, the protein was identified as specifically binding the 3’ UTR of areA mRNA. The areA transcript encodes a transcription factor involved in nitrogen metabolite repression and is subject to regulated degradation by glutamine (Gln), being highly unstable under conditions of nitrogen sufficiency. Phenotypic analysis of rrmA mutants indicated a significantly increased sensitivity to H2O2, suggesting that RrmA is also involved in the oxidative stress response. To investigate the role of RrmA protein in the regulation of transcript stability we have utilised Northern hybridisation analysis. Results show increased stability for agaA, otaA and areA transcripts in the 8710;rrmA mutant when comparison with wild type. agaA and otaA encode enzymes of arginine catabolism. However, not all transcripts subject to Gln signalled degradation are affected by this mutation. These observations indicate that the RrmA protein plays a direct role in the destabilisation of a specific subset of transcripts subject to degradation in response to a specific signal (eg Gln). The consequences of rrmA deletion on transcript levels and stability during oxidative stress are currently being investigated. An RrmA:GFP fusion was generated to investigate intracellular localisation, and possible changes that may occur in response to shifts in nitrogen regimes or oxidative stress. From this we have determined that RrmA is a highly expressed cytoplasmic protein. In the presence of ammonium (ie a rich nitrogen source) small aggregates appear which may be linked to P-bodies, the RNA-protein complexes associated with mRNA storage and degradation. Oxidative stress leads to an increase the amount of RrmA in the cell of A. nidulans.
Full conference title:
9th EUROPEAN CONFERENCE ON FUNGAL GENETICS
- ECFG 9th (2008)