IN SEARCH OF DARK HORSES - AFFINITY MATURATION OF PHAGE-DISPLACED LIGANDS

Most combinatorial libraries are 'sparse' in that only a tiny fraction of the relevant class of compounds is represented. This sparseness ca n be compensated in some measure by alternating rounds of selection wi th rounds of mutagenesis. Thus, clones are selected from the initial l ibrary by some criterion of 'fitness', such as affinity for a particul ar receptor. The selected clones are then mutagenized to generate a mu tant library, which serves as input to the next round of selection, an d so on. If the first round of selection is too stringent, rejecting a ll but the very fittest clone in the initial library (the 'initial cha mpion'), we might miss 'dark horses': clones in the initial library th at are inferior to the initial champion, yet can be mutated to even hi gher fitness than can that champion. A more thoughtful strategy is to alternate nonstringent selection with simultaneous mutagenesis of many selected clones en masse.