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Modular recognition of nucleic acids by PUF, TALE and PPR proteins.

Sequence specific binding of DNA and RNA is of fundamental importance in the regulation of cellular gene expression. Because of their modular structure repeat domain proteins are particularly well suited for these processes and have been widely adopted throughout evolution. Detailed biochemical and structural data has revealed the key residues responsible for recognition of RNA by Pumilio and FBF homology (PUF) repeat proteins and shown that the base specificity can be predicted and re-engineered. Recent work on the DNA-binding properties of transcription activator-like effector (TALE) proteins has shown that their specificity also relies on only a few key residues with a predictable code that can be used to design new DNA-binding proteins. Although less well understood, pentatricopeptide repeat (PPR) proteins contain motifs that appear to contribute to RNA recognition and comparisons to TALE and PUF proteins may help elucidate the code by which they recognize their RNA targets. Understanding how repeat proteins bind nucleic acids enables their biological roles to be uncovered and the design of engineered proteins with predictable RNA and DNA targets for use in biotechnology.