Histone mRNA is subject to 3’ uridylation and re-adenylation in Aspergillus nidulans
Post-transcriptional RNA modification is involved in various regulatory processes. In mammalian systems the addition of non-templated uridine residues to the 3’ end of the mRNA contributes to cell cycle control of histone mRNA levels. This is dependent on the nonsense mediated decay (NMD) component, Upf1, which promotes histone mRNA uridylation, leading to rapid degradation of the transcripts when DNA synthesis is blocked. We have identified a similar system in Aspergillus nidulans. However, other NMD components are also implicated, distinguishing it from the mammalian system. Genetic analysis suggests that the NMD pathway acts in parallel with the major mRNA degradation pathway which triggers decapping and 5’ – 3’ degradation to regulated histone transcript levels. Consistent with multiple RNA degradation pathways acting together, disruption of 3’ uridylation alone has a significant but limited effect. Interestingly, 3’ end degraded histone transcripts are subject to readenylation and this phenomenon extends to other transcripts. Both mRNA pyrimidine tagging and readenylation are dependent on the same terminal-nucleotidyltransferases, CutA and CutB, and we show this is consistent with the in vitro activities of both enzymes. These and previously published data demonstrate that mRNA 3’ tagging has diverse and distinct roles associated with transcript degradation and functionality.
Mark Caddick is a fungal molecular geneticist, who has worked primarily with Aspergillus nidulans as a model system. His interest in gene regulation and expression has also involved work in other organisms including plants and fish. A major area of interest over the last few years has been in transcript stability and its regulation, which lead to his current work on mRNA pyrimidine tagging. Mark is also involved in FungiDB and EupathDB, which are bioinformatics resource centres funded by the Wellcome Trust and NIH/NIAD. These provide a portal for accessing and interrogating genomic-scale datasets associated with a wide range of eukaryotic microbes. Mark has been based at the University of Liverpool in the UK for over 30 years, and is currently head of the Institute of Integrative Biology.