Arenaviridae exoribonuclease presents genomic RNA edition capacity

Elsie Yekwa; Chutima Aphibanthammakit; Xavier Carnec; Bruno Coutard; Caroline Picard; Bruno Canard; Sylvain Baize; François Ferron

In particular, previous studies on LCMV and PICV suggested that altering the NP ExoN also impacts replication, irrespective to the IFN status of the host cell [61, 67] . The structural relatedness with the Coronavirus ExoN and its implication in viral replication prompted us to investigate to which extend the arenavirus ExoN domain is able to excise unpaired nucleotides. Our enzyme activity assays demonstrate that NP-exo MOPV and NP-exo LCMV can efficiently and selectively cleave a ds RNA mimicking an erroneous replication product carrying one 3'-mismatched nucleotide (Fig 4) . Our analysis confirms that despite additional inserted structural elements, the two domains belong to the same Ribonuclease H-like superfamily. In the case of Coronaviridae, several studies have pointed to a main role of the ExoN domain of nsp14 in RNA proofreading [47] [48] [49] [50] to maintain genome stability. Structural comparison between ExoN domain of nsp14 and MOPV shows conservation of active site and main fold (Fig 5) suggesting that they have a distant but common origin. Recent work by Becares and colleagues have shown that nsp14 of Coronavirus is also involved in innate immunity modulation [68] . Therefore, these data show that at least in mutations / kb. This means that the polymerase was able to incorporate a mismatch and then elongate it. The error rate does not change between the WT and the mutant, which is consistent with the fact that we did not altered the polymerase. For both, these mutations appears along the entire L segment at an average frequency of ~10.1 % (comprised between 5 to 24 %) for the WT and of 16.6 % (comprised between 5 to 93 %) for the mutant. The fact that unlikely mutants have become prevalent, as observed at passage 10, reflect that the control over certain type of mutation have been abolished, thus implicating that ExoN is active on its own genomic RNA. In this study, it is not the particular set of mutations that is relevant but rather that a set of unlikely mutations have emerged.