Figure 2.

Distribution of amino acid substitutions. (A) Taq pol I random library contains 200,000 individual clones; sequence analysis shows that the average number of amino acid substitutions within unselected library members is four; in addition, the unselected library contains insertion, deletion, and dummy fragments. (B) There are 8,000 independent clones within the selected, active population; sequence analysis shows that the average number of amino acid changes is two, with no clones containing insertion or deletion errors. (C) Distribution of high, moderate, and low activity mutants relative to number of amino acid changes. Most mutants containing a single amino acid substitution exhibit WT-like DNA polymerase activity. Mutants with moderate or low activity contain on average two or three substitutions, respectively. Mutants with high activity generally produce greater yields during PCR and presumably have higher processivity.