Evolution of Viral Proteins Originated De Novo by Overprinting

Sabath, Niv; Wagner, Andreas; Karlin, David

Overall, we found that the differences between ancestral and de novo genes appears to decrease with time. Taxa 1-5, with the shortest distance from the origin-corresponding to the youngest de novo genes-all exhibit a similar pattern ( fig. 3) : the de novo genes show higher relative divergence with respect to their ancestral overlapping genes and weaker selective constraint. The pattern that contrasts most with that of taxa 1-5 occurs in taxa 7 and 12 (Ilarvirus and Betanodavirus, respectively), where the de novo genes have a more ancient origin. Here, the de novo genes evolve more slowly and exhibit stronger purifying selection relative to their ancestral overlapping genes ( fig. 3) . In other words, here mutations that change the sequence of the de novo proteins are more deleterious, on average, than mutations that change the sequence of the overlapping ancestral proteins.