A retroviral vector containing the lacZ a-complementation sequence (neutral mutational target) was used to score mutations appearing during a single cell infection cycle (1). Of 36561 clones analyzed, 33 carried null mutations in the target (white E. coli colonies), of which 19 were single nucleotide substitutions (four nonsense mutations), one was a double mutation (referred to as a hypermutation in the original study), and 13 were indels (including seven frameshifts). Assuming T_s = 219 (see SNV (i) estimate), m_s/n/c = 3 ´ 19 / 36561 / 219 = 7.1 ´ 10^-6. Using nonsense mutations only, T_s = 20 (see SNV (i) estimate) and thus m_s/n/c = 3 ´ 4 / 36561 / 20 = 1.6 ´ 10^-5 (we use the latter). The rate of hypermutation appears to be low and we did not attempt to calculate it since it was based on a single observation and corresponded to a double mutant, for which T_s was undetermined (the assumption that all double mutants inactivate the target cannot be made). T_i = 150 for frameshifts and T_i = 280 for other indels (see SNV (i) estimate), thus m_i/n/c = 7 / 36561 / 150 + 6 / 36561 / 280 = 1.9 ´ 10^-6, and d = 0.10.

1. Mansky, L. M. 2000. In vivo analysis of human T-cell leukemia virus type 1 reverse transcription accuracy. J. Virol. 74:9525-9531.