Broad spectrum of in vivo forward mutations, hypermutations, and mutational hotspots in a retroviral shuttle vector after a single replication cycle: substitutions, frameshifts, and hypermutations.

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Abstract
We determined the in vivo forward mutation rate in a single replication cycle for spleen necrosis virus (SNV). A method was developed to clone integrated proviruses of retroviral shuttle vectors by eploiting the tight binding of the lac operator to the lac pressor protein. The vectors contained the lacZ.alpha. gene as a reporter of mutations. Thirty-seven of the 16,867 proviruses recovered contained five classes of mutations, including substitutions and frame shifts. Runs of 9 and 10 identical base pairs and a direct repeat of 110 base pairs were mutational hotspots. In addition, two copies of a provirus contained 15 G-to-A substitutions. Such proviruses, which we name hypermutants, may arise through the action of an error-prone polymerase and could significantly contribute to the genetic varaition in retroviral populations.