Evolution of Viral Proteins Originated De Novo by Overprinting

Sabath, Niv; Wagner, Andreas; Karlin, David

Below, we first examine these three properties separately, before considering them together and synthesizing our observations. Relative Divergence Figure 3a presents for each overlap the relative sequence divergence for the pairs of ancestral proteins (red) and the pairs of de novo proteins (blue). The regression line of the ancestors (red) is nearly horizontal (although the regression coefficient is significantly different from zero, P < 0.0012) and equal to one, suggesting that on average the overlapping regions of the ancestral proteins evolve at a similar rate as the full-length ancestral proteins. In contrast, de novo proteins (blue) show a higher relative divergence than their ancestral overlapping proteins. Accordingly, the slopes of the two regression lines are significantly different (P < 3.2 Â 10 À25 ). The range of values of the relative divergences between pairs of ancestral proteins is generally narrow or moderate. For instance, the relative divergences of the de novo gene of tymovirus (taxon 11), which encodes the movement protein, range between 1.2 and 2.8 and thus vary by less than a factor three. Three notable exceptions are the youngest de novo proteins of taxa 1 and 3 (respectively, influenzavirus A PB1-F2 and betacoronavirus protein I), which exhibit a considerable range of divergences (from 0 up to 10.4).