A plaque-purified thermosensitive mutant (C5310U) was plated at 33°C and 39°C to obtain the frequency of revertants to the wild-type (1).  This mutation was approximately neutral at 33°C (a » 1) and only the C to U reversion restored growth at 39°C (T = Ts = 1).  The average revertant frequency in three isolated plaques was fs = 3.1 ´ 10-5 and c  = 2.8 (2).  Hence ms/n/c = 3 ´ 3.1 ´ 10-5 / 2.8 = 3.3 ´ 10-5.  In a second experiment, the isolated plaques were passaged once in liquid culture and the observed revertant frequency was fs = 2.3 ´ 10-5.  In the first experiment, the total number of viruses was 1.1 ´ 109 and therefore, using Equation 1 with N0 = 1, we obtain B = (1.1 ´ 109)1/2.8 = 1694.  In the second experiment, a 10-5 dilution was applied to inoculate the liquid culture and the average number of viruses after growth was 8.4 ´ 109.  Hence the amplification factor was (8.4 ´ 109) / (1.1 ´ 109) ´ 105 = 7.6 ´ 105, which corresponds to log (7.6 ´ 105) / log 1694 = 1.8 additional infection cycles.  Hence, ms/n/c = 3 ´ 2.3 ´ 10-5 / (2.8 + 1.8) = 1.5 ´ 10-5.  Taking the geometrical mean of the estimates from the two experiments, ms/n/c = 2.2 ´ 10-5.

 

 

    1.    de la Torre, J. C., C. Giachetti, B. L. Semler, and J. J. Holland. 1992. High frequency of single-base transitions and extreme frequency of precise multiple-base reversion mutations in poliovirus. Proc. Natl. Acad. Sci. USA 89:2531-2535.

    2.    Drake, J. W. and J. J. Holland. 1999. Mutation rates among RNA viruses. Proc. Natl. Acad. Sci. USA 96:13910-13913.