Summary of notable aspects pertaining to the four screens carried out in this study.

1See Materials and Methods for the method used to estimate the number of recombinants screened in each experiment. 2The mutants listed contain no additional mutations throughout the entire region examined (i.e. from –773 to +3521), except for silent mutations as indicated. 3This mutant also contains a silent mutation (G2175A). 4This mutant also contains a silent mutation (C1638A). 5This mutant also contains a silent mutation (T1488C).