Formation of an F′ Plasmid by Recombination between Imperfectly Repeated Chromosomal Rep Sequences: a Closer Look at an Old Friend (F′ 128 pro lac )

Abstract
Plasmid F′ 128 was formed by an exchange between chromosomal Rep sequences that placed lac near dinB between many pairs of Rep sequences. Plasmid F′ 128 is critical for selection-enhanced lac reversion (adaptive mutation), which requires prior lac amplification. The structure of F′ 128 supports the idea that amplification is initiated by Rep-Rep recombination and that general mutagenesis requires coamplification of dinB (error-prone polymerase) with lac .