Selfish DNA has been defined as DNA "with no phenotypic expression whose only 'function' is survival within genomes." In the 13 October Science, Ogata et al. find what appears to be selfish DNA lodged in the middle of 19 genes of Rickettsia conorii, an intracellular bacterium of ticks (Science 2000, 290:347-350). The repeats are palindromes that encode a mildly hydrophobic α helix surrounded by two extended or coil regions. This appears to be a non-functional module that has been inserted at the surface of a collection of unrelated proteins. Although the inserts probably do not provide a specific function, genetic drift from the original sequence could allow the evolution of new protein sequences, domains and functions.

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