The newly characterized colicin Y provides evidence of positive selection in pore-former colicin diversification

Two evolutionary mechanism have been proposed in the process of protein diversification of the large family of antimicrobial toxins of Escherichia coli, known a the colicins. Data from previous studies suggest that the relatively rare nuclease colicins appear to diversify primarily through the action of positive selection. Whilst the more abundant pore-former colicins appear to diversify through the action of recombination. The complete DNA sequence of the newly characterized colicin plasmid, pCo-Let, isolated from a Yanomama Indian of South America, is presented here. This plasmid encodes a newly identified pore-former colicin, colicin Y. DNA and protein sequence comparisons of the colicin Y gene cluster and the encoded proteins with those of published pore-former colicins provide the first evidence that positive selection may also act to increase pore-former colicin diversity.