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Kurt Whittemore's iGEM idea for a splicing-based Turing Mahcine: http://www.scribd.com/doc/8703987/Biological-Turing-Machine-Idea
A theoretical, polymer-based Turing Machine: http://rsfs.royalsocietypublishing.org/content/early/2012/03/21/rsfs.2011.0118.full