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ABSTRACT
It is only recently that the abundant presence of circular RNAs (circRNAs) in all kingdoms of Life, including the hyperthermophilic archaeon Pyrococcus abyssi, has emerged. This led us to investigate the physiologic significance of a previously observed weak intramolecular ligation activity of Pab1020 RNA ligase. Here we demonstrate that this enzyme, despite sharing significant sequence similarity with DNA ligases, is indeed an RNA-specific polynucleotide ligase efficiently acting on physiologically significant substrates. Using a combination of RNA immunoprecipitation assays and RNA-seq, our genome-wide studies revealed 133 individual circRNA loci in P. abyssi. The large majority of these loci interacted with Pab1020 in cells and circularization of selected C/D Box and 5S rRNA transcripts was confirmed biochemically. Altogether these studies revealed that Pab1020 is required for RNA circularization. Our results further suggest the functional speciation of an ancestral NTase domain and/or DNA ligase toward RNA ligase activity and prompt for further characterization of the widespread functions of circular RNAs in prokaryotes. Detailed insight into the cellular substrates of Pab1020 may facilitate the development of new biotechnological applications e.g. in ligation of preadenylated adaptors to RNA molecules.
Disclosure of potential conflicts of interest
No potential conflicts of interest were disclosed.
Acknowledgements
The authors thank Joëlle Kuhn for production of Pab1020 antibodies. We are grateful to Ghislaine Henneke and Didier Flament for P. abyssi cells and thank Claire Toffano-Nioche, Marc Graille and Herman Van Tilbeurgh for many stimulating discussions and suggestions during this work. We also acknowledge Ursula Liebl for critical reading of the manuscript.
Funding
This work was supported by the Agence Nationale de la Recherche grant RETIDYNA. Work in our laboratory is supported by E. Polytechnique, CNRS and INSERM. Funding for open access charge: INSERM.
