Proteins synthetic combinatorial library approach

As mentioned above, once freed from the constraints of a complementary strand, polynucleotides can fold into a wide range of three-dimensional structures, leading to a diverse array of functions. Two specific types of functional polynucleotides are (1) aptamers, which bind noncovalently but selectively to ligands and (2) enzymes, which catalyze chemical reactions similar to protein enzymes. While a few examples of both natural aptamers and enzymes have been discovered, far more have been identified from synthetic combinatorial libraries through in vitro selection methods. The general approach to selection of functional polynucleotides is described below, followed by specific examples of nucleic acid-based aptamers and enzymes. 

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