2A and 2A-like Sequences: Distribution in Different Virus Species and Applications in Biotechnology.

2A is an oligopeptide sequence that mediates a ribosome "skipping" effect and can mediate a co-translation cleavage of polyproteins. These sequences are widely distributed from insect to mammalian viruses and could act by accelerating adaptive capacity. These sequences have been used in many heterologous co-expression systems because they are versatile tools for cleaving proteins of biotechnological interest. In this work, we review and update the occurrence of 2A/2A-like sequences in different groups of viruses by screening the sequences available in the National Center for Biotechnology Information database. Interestingly, we reported the occurrence of 2A-like for the first time in 69 sequences. Among these, 62 corresponded to positive single-stranded RNA species, six to double stranded RNA viruses, and one to a negative-sense single-stranded RNA virus. The importance of these sequences for viral evolution and their potential in biotechnological applications are also discussed.

Evolutionary origin of 2A-like sequences in Totiviridae genomes.

In recent years there has been a significant increase in the number of new species potentially belonging to the Totiviridae family. Most of these new viruses have not yet been covered by the Committee on Taxonomy of Viruses (ICTV) official classification. In this study, a phylogenetic analysis including new sequences of Totiviridae candidates revealed a clade including Giardiavirus and a great diversity of new totiviruses, which infect arthropods, protozoa and mollusc. This expanded Giardiavirus clade comprises two monophyletic groups, one of them including Giardia lamblia virus (GLV) grouped with viruses that infect arthropods and vertebrates (GLV-like group), and the other includes the previously proposed Artivirus group (IMNV-like group). A screening of the members of the GLV-like group in search of genomic elements already described in IMNV-like group revealed the existence of sites with a high propensity to become 2 A-like oligopeptides, mainly in a specific subgroup of arthropod viruses, suggesting that these viruses preserved ancestral characteristics. The existence of these "pseudo 2 A-sites" associated to phylogenetic reconstruction indicates that these sequences appear at a decisive stage for viral evolution. If they are changed to functional 2 A-like sequences, an irreversible route to increase the genome complexity will be initiated.