Strain and plasmid list.

aAll strains are isogenic with MG1655 with the genotype F-rph-1.
bThe dam gene was cloned using the Gateway Cloning Technology and methods provided by the manufacturer (Invitrogen). The dam gene was amplified by PCR with Triplemaster (Eppendorf), primers 5′-GGGGACAAGT TTGTACAAAA AAGCAGGCTT CACAGCCGGA GAAGGTGTAA TTAGTTAGTC AGCATGAAGA AAAA and 5′-GGGGACCACT TTGTACAAGA AAGCTGGGTT TATTTTTTCG CGGGTGAAAC GACT and the chromosomal template DNA derived from E. coli K-12 MG1655 (Masterpure DNA purification kit, Epicentre). After purification (Qiagen PCR purification kit), the dam gene was inserted into vector pDONR201 and subcloned from this plasmid into the destination vector pSTL360 [64], a derivative of pBAD18 [65] with an arabinose-regulated promoter. Plasmids were recovered by transformation into E. coli K-12 strain DH5α. The presence of intact dam in these plasmids was confirmed by DNA sequence analysis.