Adaptive evolution by spontaneous domain fusion and protein relocalization.

Knowledge of adaptive processes encompasses understanding the emergence of new genes. Computational analyses of genomes suggest that new genes can arise by domain swapping; however, empirical evidence has been lacking. Here we describe a set of nine independent deletion mutations that arose during selection experiments with the bacterium Pseudomonas fluorescens in which the membrane-spanning domain of a fatty acid desaturase became translationally fused to a cytosolic di-guanylate cyclase, generating an adaptive 'wrinkly spreader' phenotype. Detailed genetic analysis of one gene fusion shows that the mutant phenotype is caused by relocalization of the di-guanylate cyclase domain to the cell membrane. The relative ease by which this new gene arose, along with its functional and regulatory effects, provides a glimpse of mutational events and their consequences that are likely to have a role in the evolution of new genes.