Error-Prone Polymerase, DNA Polymerase IV, Is Responsible for Transient Hypermutation during Adaptive Mutation in Escherichia coli

Abstract
The frequencies of nonselected mutations among adaptive Lac+ revertants of Escherichia coli strains with and without the error-prone DNA polymerase IV (Pol IV) were compared. This frequency was more than sevenfold lower in the Pol IV-defective strain than in the wild-type strain. Thus, the mutations that occur during hypermutation are due to Pol IV.