Changes in the sequence are shown in italic letters. Incorporation of the metA mutations into the E. coli

chromosome The mutated BV-6 nmr metA genes were transferred to the E. coli JW3973 (ΔmetA) chromosome as previously described [11] using the λ Red recombination system [32]. Construction of the ∆dnaK::cat and [(∆clpX-lon)::cat, ∆hslVU1172::tet] mutants The structural gene dnaK in the WE strain was replaced with the chloramphenicol resistance gene using the λ Red recombination system [32]. A disruption cassette was synthesized through PCR using the forward primer dnaK1 (CAGACTCACAACCACATGATGACCGAATATATAGTGGAGACGTTTAGGTTGGCAGCATCACCCGAC), the reverse primer dnaK2 (CTTCTTCAAATTCAGCGTCGACAACATCGTCATCTTTCGCGTTGTTTGCGTAGCACCAGGCGTTTAAGG), Vent polymerase and the plasmid pACYC184 as a template (homologous sequences are shown in italic letters). Replacement of the dnaK gene was confirmed through PCR analysis of the chromosomal DNA of the WE∆dnaK strain. A temperature-sensitive phenotype of strain WE∆dnaK at 37 and 40°C (data not shown) was rescued with the plasmid pDnak carrying the dnaK gene under the endogenous P dnaK promoter amplified from

the genomic DNA of WE strain using the primers dnaK3 (CGCCTCCTCGAGCATATCGCGAAATTTCTGCGC) and dnaK4 (GANT61 CCCGTGTCAGTATAATTACCC) and cloned into the XhoI/SmaI restriction sites of the plasmid vector pACYC177. The ∆dnaK::cat mutants of strains L124 and Y229 were obtained through transduction with P1vir using the WE∆dnaK donor strain. The double mutant ∆clpX-lon::cat was constructed after replacing the structural genes in the WE strain with the chloramphenicol resistance Diflunisal click here gene as previously described [32]. The primers ClpX1-forward (GCATTTGCGTCGTCGTGTGCGGCACAAAGAACAAAGAAGAGGTTTTGACCCGTTGGCAGCATCACCCGAC) and Lon1-reverse (CCTCAATGCGCTTCACAGGATGAATGTCCAGATCGGCAATTACGTTGTCAGGGTAGCACCAGGCGTTTAAGG),

Vent polymerase and the plasmid pACYC184 were used to synthesize the chloramphenicol resistance gene flanked by the 51 nucleotides upstream of the clpX gene and the 52 nucleotides corresponding with the region 2241–2293 of the lon gene (homologous sequences are underlined). The gene hslVU in the double mutant ∆clpX-lon was replaced through transduction using P1vir grown on the ∆hslVU1172::tet donor (ME7970), an in-kind gift from the Institute of Genetics, Japan. The resulting strain WE(P-) demonstrated temperature sensitive growth at 42°C similar to the previously described triple protease-deficient E. coli mutant KY2266 [16]. The normal growth of the WE(P-) mutant at 42°C was restored through transformation with the plasmid pPP1 harboring the clpX-lon genes under the endogenous P clpX promoter amplified from the genomic DNA of WE strain using the primers ClpX4 (CGCCTCCTCGAGCATGCCCGTGAAATTCTG) and Lon4 (GCCATCTAACTTAGCGAGAC) and cloned into the XhoI/SmaI restriction sites of the plasmid vector pACYC177.