Lactose operon sequences from: Nature reserves suppress evolutionary rescue from extinction

Escherichia coli K-12 GM4792 is incapable of utilizing lactose (lac-). However, when cultured in M9 medium containing both lactose and glucose as mixed carbon sources, lactose-utilizing reverse mutations (lac+) can be observed. We isolated and sequenced single clones of both lac- and lac+, and identified the molecular basis underlying the lactose utilization. Methods Lactose operon sequences from single clones that are incapable of utilizing lactose (lac-) and those with lactose-utilizing reverse mutations (lac+) were obtained by PCR and sequencing, and these sequences were subsequently aligned.