Escherichia coli strains were grown in Luria–Bertani (LB) medium at 37 °C with either shaking at 180 r.p.m. or statically. Yersinia pseudotuberculosis YpIII and the isogenic mutant strains were grown in YLB medium (Yersinia LB, LB with half the concentration of NaCl) at 28 °C unless otherwise stated. Antibiotics (where appropriate) were applied at the following concentrations: Epigenetics inhibitor 30 μg mL−1 chloramphenicol, 15 μg mL−1 nalidixic acid and 100 μg mL−1 ampicillin. ΔsraG was constructed using the suicide plasmid pDM4 (O’Toole et al., 1996). The +1 site and terminator of SraG was

determined by annotation in the NCBI database. To delete the +1 to +184 region of the sraG gene, a 510-bp fragment upstream of the +1 of sraG with SalI and EcoRI and a 505-bp fragment downstream of the +184 of sraG with EcoRI and BglII were amplified by PCR (all primers are listed in Supporting Information, Table S1). The fragments were digested with specific restriction enzymes and inserted into the pDM4 plasmid by T4 DNA ligase. The recombinant plasmid was transformed into E. coli S17-1 λ-pir. Transconjugation was performed as described previously

(Hu et al., 2009). WT YpIII was used as the parental strain to obtain ΔsraG in which nucleotides +1 to 184 of the sraG gene were replaced by the EcoRI site. Mutants were verified by both PCR and sequencing. To construct the SraG complementing plasmid, a plasmid named pRO-SraG was constructed based on the pMD 18-T Vector (TaKaRa). First, the DNA fragment was amplified C1GALT1 http://www.selleckchem.com/products/BIBW2992.html by PCR to obtain the plasmid backbone containing the

lac promoter, ampicillin resistance cassette, pUC replicon and lacZ terminator. The sraG gene was amplified using primers psraGoverlapF and psraG-ER (Table S1). The sense primer anneals to the +1 site of sraG and carries a short overlapping fragment with plasmid backbone. The antisense primer binds to the region ~100 nt downstream of the SraG terminator and adds an EcoRI site to the PCR product. Overlapping PCR and EcoRI digestion were used to ligate the plasmid backbone and sraG to construct pRO-SraG, which was then electrotransformed into the ΔsraG strain. To construct the translational gene::lacZ fusion, the antisense primer was designed to pair with the exact 3′-end of the coding sequence (CDS), omitting the stop codon with the SpeI site, and the sense primer was designed to pair with the region about 500 nt upstream of the stop codon with the SalI site. The PCR fragment was digested with SpeI and SalI and ligated into the pDM4-lacZ plasmid (Hu et al., 2009). The single-copy lacZ fusion was obtained by transconjugation as described previously (Hu et al., 2009).