The importance of protein arginine methylation in the regulation of cell function is currently emerging. Among the multitude of substrates of protein arginine methyltransferases (PRMTs) are proteins involved in RNA processing, regulation of transcription, translation, signal transduction, apoptosis, and subcellular transport. It has also been shown that core histones are methylated by PRMTs in vivo and that histone arginine methylation takes part in transcriptional regulation. In the filamentous fungus Aspergillus nidulans three PRMTs (RmtA, RmtB, and RmtC) are present. In order to study PRMT-dependent processes we generated deletion mutants via a gene targeting strategy. Deletion strains could be achieved for all PRMT genes, thus none of these genes alone is essential for the viability of A. nidulans. Phenotypic analysis revealed that growth of rmtA and rmtC mutants was significantly reduced when acetate was provided as sole carbon source, or when strains were grown under oxidative stress inducing conditions. We further could demonstrate that catalytic activity of RmtA is crucial for the oxidative stress defense in A. nidulans. Moreover, rmtC mutants exhibited decreased ability to grow at elevated temperatures. Biochemical analysis revealed substrate specificity of RmtA for histone H4. Further, methylation of H3 was dependent on the presence of both, RmtB and RmtC, indicating a cooperative role of these enzymes in establishing this modification in vitro. Interestingly, also H2B methylation could be detected, however, the methylation status was not affected by either deletion, indicating the presence of an additional yet unidentified enzymatic activity. Taken together, our results substantiate the physiological significance of protein arginine methylation in A. nidulans. Generated deletion mutants will be valuable tools for further biochemical and genetic studies on the function of this modification in A. nidulans, and may also improve our understanding of the role of protein arginine methylation in higher eukaryotes.
Full conference title:
9th EUROPEAN CONFERENCE ON FUNGAL GENETICS
- ECFG 9th (2008)