An amber mutant was grown in cells encoding an amber suppressor (permissive cells) and plated in normal cells (non-permissive) after a single burst to score the appearance of amber revertants (1). An estimate of m_s = 2.7 ´ 10^-6 s/r was obtained using the null-class method. There are eight possible ways of reverting an amber mutation through single nucleotide substitutions. However, some might be lethal and hence not observable. For p_L = 0.2-0.4, T_s = 4.8-6.4. Taking T_s = 5.6, m_s/n/r = 3 ´ 2.7 ´ 10^-6 / 5.6 = 1.4 ´ 10^-6. Error in this estimate comes mainly from the undetermined T-value, which could produce a maximal underestimation of 5.6-fold and a maximal overestimation of 1.4-fold.

1. Chao, L., C. U. Rang, and L. E. Wong. 2002. Distribution of spontaneous mutants and inferences about the replication mode of the RNA bacteriophage f6. J. Virol. 76:3276-3281.