A retroviral vector containing the Herpes simplex virus tk gene (a neutral mutational target) and the neo gene was used to score mutations appearing during a single cell infection cycle by selecting tk null mutants with bromouridine and total virus-carrying cells with G418 (2), giving f / c = 0.088.  According to Drake et al. (1), of 244 tk- mutants, 114 were gross rearrangements and arose in a mutational target of 2620 bases.  Assuming that all gross rearrangements inactivated the tk gene, the mutation rate to these changes 0.088 ´ 114 / 244 / 2620 = 1.6 ´ 10-5 rearrangements/s/c.  The remaining 130 changes were small mutations and arose in a target of 1128 bases.  Among 49 small mutants sequenced, 28 were indels.  Hence, mi/n/c = 0.088 ´ 130 / 244 ´ 28 / 49 / 1128 = 2.4 ´ 10-5.  Among nucleotide substitutions, three were nonsense mutations.  Given that Ts = 76 for nonsense substitutions in this gene, ms/n/c = 3 ´ 0.088 ´ 130 / 244 ´ 3 / 49 / 76 = 1.1 ´ 10-4.  The indel fraction is thus d = (1.6 ´ 10-5 + 2.4 ´ 10-5) / (1.1 ´ 10-4 + 1.6 ´ 10-5 + 2.4 ´ 10-5) = 0.27.

 

 

    1.    Drake, J. W., B. Charlesworth, D. Charlesworth, and J. F. Crow. 1998. Rates of spontaneous mutation. Genetics 148:1667-1686.

    2.    Parthasarathi, S., A. Varela-Echavarria, Y. Ron, B. D. Preston, and J. P. Dougherty. 1995. Genetic rearrangements occurring during a single cycle of murine leukemia virus vector replication: characterization and implications. J. Virol. 69:7991-8000.