Figure 2: Effects of residue changes in the Walker B motif on virus yield.

Left table lists the mutants tested and a color-key is used to indicate the range of detected degrees of impairment expressed in terms of phage yield in plaque forming units per cell relative to WT (where the WT activity is defined to be 1). Right table lists the color-key that indicates the relative phage yields. Dark gray color is used to designate cases where no phage yield was detected (i.e., below the level of sensitivity of the assay). Pairs of codons were mutagenized for codons 174-175, and for 176-177, though single codon changes were made for the V174P, A175L, G176S, and Y177V mutants. Wildtype terminase sponsored yields of 3 – 10 λ Aam/induced cell. Two of the mutants, V174V+A175L and V174P+A175A were effectively single mutants because each contained a same-sense codon change in addition to a mutation causing a residue change. The same-sense changes were to codons with usage frequencies similar to that of the wildtype codon. For example, the codon changes producing TerL^λ-V174V+A175L were GUG+GCG→GUA+CUG. The codon usages in E. coli for the wildtype and same-sense valine codons are 2.4% and 1.2%, respectively. The GUA codon is occurs twice in the wildtype A gene, indicating that the change to this codon is unlikely to affect gene expression. Accordingly, these two mutants are listed as single mutants V174P and A175L.