Destabilizing mutations encode nongenetic variation that drives evolutionary innovation

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Science  30 Mar 2018:
Vol. 359, Issue 6383, pp. 1542-1545
DOI: 10.1126/science.aar1954

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Nongenetic variation drives viral evolution

Bacteriophage λ is a virus that infects bacteria by exploiting various membrane proteins in a well-characterized manner. Petrie et al. show how the evolution of variable folding conformations of isogenic proteins, which do not differ in their genetic sequences, contributed to λ's ability to exploit an additional host receptor for infection. Because the protein can take on two shapes, this genotype can have two phenotypes. Natural selection may thus be able to act on this nongenetic heterogeneity to connect phenotypic heterogeneity, evolvability, and protein stability.

Science, this issue p. 1542


Evolutionary innovations are often achieved by repurposing existing genes to perform new functions; however, the mechanisms enabling the transition from old to new remain controversial. We identified mutations in bacteriophage λ’s host-recognition gene J that confer enhanced adsorption to λ’s native receptor, LamB, and the ability to access a new receptor, OmpF. The mutations destabilize λ particles and cause conformational bistability of J, which yields progeny of multiple phenotypic forms, each proficient at different receptors. This work provides an example of how nongenetic protein variation can catalyze an evolutionary innovation. We propose that cases where a single genotype can manifest as multiple phenotypes may be more common than previously expected and offer a general mechanism for evolutionary innovation.

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