Structures and exoribonuclease activity fonctions in arenavirus and coronavirus

RNA viruses encode dedicated protein machinery required through the viral life cycle. Some enzymatic activities are generally associated with RNA viruses such as RNA- or DNA-dependent RNA polymerases, RNA helicases or proteases. Some viral enzyme activities are however unique to some viral families. This is the case of two 3'-5' exoribonuclease activities identified in arenavirus and coronavirus proteomes. Arenaviruses have a segmented ambisense single stranded RNA genome of negative polarity while coronaviruses have a positive single-stranded genomic RNA. Although both enzymes belong to the same exo(ribo)nuclease superfamily, available data indicate that they are involved in very different pathways. Indeed, the exoribonuclease activity carried by the arenavirus nucleoprotein seems to counteract the innate immunity antiviral response while the exoribonuclease activity carried by the coronavirus nsp14 protein is likely involved in a unique RNA repair mechanism. In this review, we present our current knowledge about these two viral enzymes and their functions in the viral life cycle.