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 div ersification of the large family of antimicrobial toxins of Escherichia col i, known a the colicins. Data from previous studies suggest that the relati vely rare nuclease colicins appear to diversify primarily through the actio n of positive selection. Whilst the more abundant pore-former colicins appe ar to diversify through the action of recombination. The complete DNA seque nce of the newly characterized colicin plasmid, pCo-Let, isolated from a Ya nomama Indian of South America, is presented here. This plasmid encodes a n ewly identified pore-former colicin, colicin Y. DNA and protein sequence co mparisons 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.