TABLE 1.
Effect of amino acid replacement at positions 1, 5, and 6 of the putative recognition helix on the binding activity of CopF to the 31-bp wt operator
| Amino acid at recognition helix position:
|
% Residual activity with the mutant/that with the wta | % Probabilityb of HTH formation | ||
|---|---|---|---|---|
| 1 | 5 | 6 | ||
| Ile | 15.8 | 25 | ||
| Leu | 15.3 | 25 | ||
| Arg | 100 | 71 | ||
| Gln | 11.6 | 50 | ||
| Pro | 14.9 | 25 | ||
| Thr | 24.1 | 25 | ||
| Ser | 100 | 71 | ||
| Gln | 14.8 | 50 | ||
| Pro | 11.9 | 0 | ||
| Arg | 100 | 71 | ||
a
Phages bearing mutant CopF were prepared and tested by a filter binding assay with labeled operator. Residual activity corresponds to the ratio of the radioactivity bound by the phage displaying the mutant relative to that of the phage displaying the wt protein. In this experiment, the background radioactivitiy in control reaction mixtures free of phages corresponded to 11.5% of the radioactivity found with the phage carrying the wt protein.
b
The probability of HTH motif formation in mutant CopF protein is given according to the method of Dodd and Egans (11).