Table 1.

Strains and plasmids

Strain or plasmid	Relevant properties	References
E. coli
DH5α	General-purpose strain	Hanahan (1983)
MT616	MT607, pRK600, CmR	Finan et al. (1986)
S. meliloti
Rm1021	SU47, SmR
Rm7095	Rm1021 exoR95 : : Tn5, NmR	Doherty et al. (1988)
Rm7096	Rm1021 exoS96 : : Tn5, NmR
SmHC20	exoR95exoS*, NmR	This work
SmHC21	exoR95exoSsupA, NmR	This work
Plasmids
pMB393	Cloning vector, SpR	Gage et al. (1996)
pHC77	pMB393 carrying the exoX–exoY intergenic region and exoY : : gfp fusion	Cheng & Yao (2004)
pHC505	pMB393 with the fusion of the exoR promoter (−20 to −1 region) and the gfp gene	This work
pHC501	pMB393 with the fusion of the exoR promoter (−662 to −1 region) and the gfp gene	This work
pHC514	pPexoRgfp, pMB393 with the fusion of the exoR promoter (−325 to −1 region) and the gfp gene	This work
pHC548	pMB393 with the fusion of the exoR promoter (−662 to −353 and −20 to −1 region) and the gfp gene	This work
pSW213	Cloning vector, IncP-derived, lacIQ, PlaclacZ, TcR	Mantis & Winans (1993)
pHC530	pPlacexoR, pSW213 with the exoR gene expressed from the inducible lac promoter	This work
pHC556	pPlacexoRΔsp, pSW213 with a mutated exoR lacking its signal peptide sequence expressed from the inducible lac promoter	This work
pHC560	pPlacexoS, pSW213 with the exoS gene expressed from the inducible lac promoter	This work
pRK600	Helper plasmid, CmR	Finan et al. (1986)
pJK19-1	GFP(S65T), Apr	Gift from P. Silver