The Escherichia coli Histone-like Protein HU Has a Role in Stationary Phase Adaptive Mutation

Abstract

Abstract Stationary phase adaptive mutation in Escherichia coli is thought to be a mechanism by which mutation rates are increased during stressful conditions, increasing the possibility that fitness-enhancing mutations arise. Here we present data showing that the histone-like protein, HU, has a role in the molecular pathway by which adaptive Lac+ mutants arise in E. coli strain FC40. Adaptive Lac+ mutations are largely but not entirely due to error-prone DNA polymerase IV (Pol IV). Mutations in either of the HU subunits, HUα or HUβ, decrease adaptive mutation to Lac+ by both Pol IV-dependent and Pol IV-independent pathways. Additionally, HU mutations inhibit growth-dependent mutations without a reduction in the level of Pol IV. These effects of HU mutations on adaptive mutation and on growth-dependent mutations reveal novel functions for HU in mutagenesis.