Human APOBEC1 induces a mutator phenotype in bacteria. (A) Frequency of rifampicin-resistant clones in cultures of Escherichia coli transformed with APOBEC1 expression constructs (rat or human) or empty vector. Each point represents the mutation frequency of an independent overnight culture. The median mutation frequency is indicated. (B) Distribution of independent rpoB point mutations identified in rifampicin-resistant clones from bacteria transformed with human APOBEC1 (black changes above the sequence), rat APOBEC1 (black changes below the sequence), or empty plasmid (brown changes below the sequence). The number of independent colonies is indicated in parentheses.