Table 1. Bacterial strains and plasmids used in this work.

Strain or plasmid	Relevant characteristic(s)	Source or reference
Strains
DH5α	E. coli supE4 ΔlacU169 (φ80 ΔlacZ ΔM15) hsdR17, recA1, endA1, gyrA96, thi-1, relA1	Clontech
MC1061	E. coli F− Δ(ara-leu)7697 [araD139] B/r Δ(codB-lacI)3 galK16 galE15 λ− e14− mcrA0 relA1 rpsL150 (StrR) spoT1 mcrB1 hsdR2(r−m+)	CGSC
BL21 (DE3) pLysS	E. coli F− dcm ompT lon hsdS(rB−mB−) galλ(DE3) carring pLysS plasmid, CmR	Stratagene
LT2	S. Typhimurium wild type strain	ATCC
UA1907	S. Typhimurium ΔcheWΩcat. CmR	This work
UA1908	S. Typhimurium ΔcheW	This work
UA1910	S. Typhimurium ΔcheR	This work
UA1915	S. Typhimurium ΔcheR ΔcheW	This work
UA1913	S. Typhimurium ΔcheR ΔrecA	This work
UA1927	S. Typhimurium ΔrecAΩ,cat. CmR	This study
UA1928	S. Typhimurium ΔcheB	[29]
UA1929	S. Typhimurium ΔcheY	[29]
UA1930	S. Typhimurium ΔcheW ΔrecA	This work
UA1931	S. Typhimurium ΔrecA	This work
Plasmids
pKOBEGA	Vector containing the λ Red recombinase system, Ampr, temperature sensitive	Generous gift of Prof. G. M. Ghigo, [33]
pKD3	Vector carrying FRT-Cm construction, AmpR, CmR	[31]
pCP20	Vector carrying FLP system, OriVts, AmpR	[31]
pGEM-T	Cloning Vector; AmpR	Promega
pGEX 4T-1	Expression vector carrying the Ptac IPTG - inducible promoter and the lacIq gene; GST fusion tag, AmpR	Amersham Biosciences
pUA1108	pGEX 4T-1 derivative plasmid carrying without the GST fusion tag, carrying only the Ptac promoter and the lacIq gene; used as overexpression vector, AmpR	This work
pUA1109	pUA1108 derivative containing the native S. Typhimurium recA gene under the control of the Ptac promoter, AmpR.	This work
pUA1127	pUA1108 derivative vector carrying the eYFP::cheR fusion, AmpR	This work
pUA1130	pUA1108 derivative containing the native S. Typhimurium recA gene under the control of the Ptac promoter, AmpR.	This work
pUA1131	pUA1108 derivative overexpression vector carrying the cheW-FLAG gene	This work
pB2HΔα	pACYCDuet-1 derivative vector with the E. coli Δα β-galactosidase fragment under the control of the Ptac promoter	BCCM/LMBP, [36]
pB2HΔω	pACYCDuet-1 derivative vector with the E. coli Δω β-galactosidase fragment under the control of the Ptac promoter	BCCM/LMBP, [36]
pUA1114	pB2HΔα derivative vector contaning the Δα-recA fusion	This work
pUA1115	pB2HΔω derivative plasmid contaning the Δω-recA fusion	This work
pUA1116	pB2HΔα derivative vector contaning the Δα-cheW fusion	This work
pUA1117	pB2HΔω derivative plasmid contaning the Δω-cheW fusion	This work
pUA1118	pB2HΔα derivative plasmid contaning the Δα-amyA fusion, used as a control in two hybrid assays.	This work
pUA1119	pB2HΔω derivative plasmid contaning the Δω-dnaE fusion, used as a control in two hybrid assays.	This work