  We investigate the sensitivity of production rates (activities) of the
regulatory proteins CI (repressor) and Cro at the right operator (O_R}) of
bacteriophage lambda. The DNA binding energies of CI, Cro, and RNA polymerase
are perturbed to check the uncertainty of the activity, due to the experimental
error, by means of a computational scattering method according to which the
binding energies are simultaneously chosen at random around the literature
values, with a width corresponding to the experimental error. In a grand
canonical ensemble, with the randomly drawn protein-DNA binding energies as
input, we calculate the corresponding activities of the promoters P_RM and P_R.
By repeating this procedure we obtain a mean value of the activity that roughly
corresponds to wild-type (unperturbed) activity. The standard deviation
emerging from this scheme, a measure of the sensitivity due to experimental
error, is significant (typically > 20% relative to wild-type activity), but
still the promoter activities are sufficiently separated to make the switch
feasible. We also suggest a new compact way of presenting repressor and Cro
data.
