**3.1 Copy-choice recombination**

**Figure 2** indicates how an accurate undamaged progeny single-stranded genome can be generated from a damaged parental genome by strand-switching (copychoice) recombination. As shown in this **Figure 2**, (1) during synthesis of a progeny strand by a replicative polymerase, a damage in the (green) template strand (strand being copied) blocks polymerase progression. (2) If another (orange) homologous template is available, the polymerase may switch templates, thereby bypassing the damage. (3) The newly synthesized strand may then release from the second template strand. (4) The newly synthesized strand can return and pair with the original template. (5) The polymerase may then complete the replication using the original template. (6) These steps can generate a new recombinant genome without damage [9, 34].

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**Figure 3.**

*licenses/by-sa/4.0)*

*Origin of DNA Repair in the RNA World DOI: http://dx.doi.org/10.5772/intechopen.93822*

**3.2 Poliovirus and coronavirus**

Poliovirus (Family *Picornaviridae*; Genus *Enterovirus*) is a positive ssRNA ((+) ssRNA) virus that can undergo genetic recombination when there are at least two ssRNA viral genomes in the same host cell. RNA recombination is considered to be a major driving force in determining the course of poliovirus evolution [35]. RNAdependent RNA polymerase (RdRp), an enzyme encoded in the viral genome, catalyzes genome replication. Kirkegaard and Baltimore [34] presented results strongly supporting a copy-choice mechanism for RNA recombination for poliovirus. By this mechanism the RdRp switches between (+)ssRNA templates during synthesis of the progeny negative strand (−)ssRNA (**Figure 2**). Recombination in RNA viruses is considered to be an adaptive mechanism for maintaining genome integrity [36].

To regenerate the next generation of (+)ssRNA strands, the (−)ssRNA strands are also copied and this may also be accompanied *infrequently* by strand switching [34]. When cells are infected by two or more viruses containing genome damage the viruses may undergo multiplicity reactivation. Polioviruses are able to undergo

*Coronavirus. Modified from https://commons.wikimedia.org/wiki/File:3D\_medical\_animation\_coronavirus\_ structure\_vie.png with license https://www.scientificanimations.com/CC BY-SA (https://creativecommons.org/*

**Figure 2.** *Copy-choice recombination.*
