Mutant distributions and the error threshold.

<p>(A) The majority of viruses in a wild-type population has few mutations and is viable Some viruses, bearing a higher mutational load, are nonviable and considered beyond the threshold of error catastrophe (shown in green). Small increases in mutation frequency, mediated by host APOBEC proteins or exogenous mutagen, push the distribution to the right, past the error threshold. The number of errors per genome is sufficiently high to lethally mutate a majority of the population. (B) A high fidelity polymerase results results in a narrower quasispecies situated farther from the error threshold. This population is more resistant to the effect of mutagen, because it does not accumulate as many mutations, as the wild type does not cross the error threshold. Figure adapted from Crotty et al. <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1001005#ppat.1001005-Crotty1" target="_blank">[42]</a>.