Figure 3.

High mutability of motif A. To test the importance of this conservation, Residues L⁶⁰⁵ to R⁶¹⁷ (D⁶¹⁰YSQIELR⁶¹⁷) were randomly mutated such that each contiguous amino acid can be replaced by potentially any of the other 19. (A) The degree of mutability of each amino acid within motif A from all active clones (>10% to 200% activity relative to WT) complementing an E. coli DNA polymerase I temperature-sensitive strain. Amino acid substitutions at the locus are listed, along with the number of times each substitution is observed. (B) Mutations in clones exhibiting high activity (66% to 200% WT). (C) Mutations in clones containing a single amino acid substitution followed by activity relative to WT. Clones containing the same amino acid substitution contain unique silent changes at other loci; thus, they represent independent sequences.