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). In total, 11 / 18009 clones carried null mutations (white E. coli colonies), of which three were nucleotide substitutions (two nonsense mutations) and eight were indels (four frameshifts). Assuming T_s = 219 (see SNV (i) estimate), m_s/n/c = 3 ´ 3 / 18009 / 219 = 2.3 ´ 10^-6. Using nonsense mutations only, T_s = 20 (see SNV (i) estimate) and thus m_s/n/c = 3 ´ 2 / 18009 / 20 = 1.7 ´ 10^-5. We used the latter estimate. T_i = 150 for frameshifts and T_i = 280 for other indels (see SNV (i) estimate), thus m_i/n/c = 4 / 18009 / 150 + 4 / 18009 / 280 = 2.3 ´ 10^-6, and d = 0.12.

1. Mansky, L. M. and H. M. Temin. 1994. Lower mutation rate of bovine leukemia virus relative to that of spleen necrosis virus. J. Virol. 68:494-499.