**Strains** |

*E. coli* |

BW20767 | RP4-2-*tet*:Mu-1*kan*::Tn*7* integrant *leu-63*::IS*10 recA1* | Metcalf *et al.* (1996) |

| *creC510 hsdR17 endA1 zbf*-*5 uidA*(Δ*MluI*):*pir*^{+}*thi* |

DH5α | F^{–}φ80d*LacZ*ΔM15 *recA1 endA1 gyrA96* thi-1 *hsdR17* (rK^{–}mK^{+}) *supE44 relA1 deoR*Δ(*lacZYA*–*argF*)U169 | Life Technologies |

DH10B | F^{–}*mcrA*Δ(*mrr*–*hsdRMS*–*mcrBC*) φ80d*LacZ*ΔM15 *lac*X74 *endA1* *recA1 deoR*Δ(*ara*, *leu*)7697 *araD139 galU galK nupG rpsL* | Life Technologies |

HB101 | F^{–}*thi*-1*hsdS20* (r_{B}^{–}m_{B}^{–}) *supE44 recA13 ara*-14 *leuB6 proA2 lacY1 rpsL20* (Sm^{r}) *xyl*-*5 mtl-1* | Boyer and Roulland-Dussoix (1969) |

MT616 | *pro-82 thi*-1 *hsdR17 supE44 endA1 recA56* (pRK600); Cm^{r} | Finan *et al.* (1986) |

*S. meliloti* |

RT3-27 | *actP*::Tn*5* mutant of WSM419; Cu^{s}, Cm^{r}, Km^{r} | This study |

WSM419 | Acid^{t} Sardinian isolate; Cm^{r}, Cu^{t} | J. Howieson^{a} |

*R. leguminosarum* bv. *viciae* |

PW711 | Spontaneous Sm^{r} mutant of WSM710 | Reeve *et al.* (1999) |

WR1-14 | *actP*::Tn*5* mutant of WSM710; Cu^{s}, Km^{r}, Sm^{r} | This study |

WR1870 | *hmrR*:Gm mutant of WSM710; Cu^{t}, Gm^{r} | This study |

WR1871 | *hmrR*:Gm mutant of WSM710; Cu^{t}, Gm^{r} | This study |

WR1880 | WR1870 (pMUE668); Tc^{r}, Gm^{r}, Km^{r} | This study |

WR1885 | WR1875 (pMUE668); Tc^{r}, Gm^{r}, Km^{r} | This study |

WSM710 | Acid^{t} Japanese isolate; Cu^{t} | J. Howieson |

**Plasmids** |

pBR01 | pFUS1 derivative constructed by replacing the *Pst*I/*Not*I fragment containing *gusA* with the *Pst*I/*Not*I MCS from pUK21; Tc^{r} | Beau Fenner^{a} |

pBR322 | Cloning vector; Ap^{r} Tc^{r} | Bolivar *et al.* (1977) |

pCRS433 | Broad host range vector; Tc^{r} | Reeve *et al.* (1999) |

pCRS487 | pUT::mTn*5*-GNm; Ap^{r}, Km^{r} | Reeve *et al.* (1999) |

pFUS1 | pCRS433 derivative containing a promoterless *gusA*; Tc^{r} | Reeve *et al.* (1999) |

pJQ2ΩS | pJQ200SK derivative constructed by replacing a blunted *Eco*RV/*Sph*I fragment containing *aacC1* with a blunted *Hin*dIII fragment containing ΩSm/Sp; Sm/Sp^{r}, Suc^{s} | Sophie Rome |

pJQ200SK | Gene replacement vector; Gm^{r}, Suc^{s} | Quandt and Hynes (1993) |

pNK52 | pSW213 containing *actP* and *hmrR* on a 4.8 kb *Hin*dIII fragment; Tc^{r} | This study |

pNK57 | pFUS1 containing a mutated *actP* and wild-type *hmrR* on a 4.2 kb *Hin*dIII/*Apa*I fragment (Fig. 1); Tc^{r} | This study |

pNK77 | pFUS1 containing a 4.8 kb *S. meliloti Hin*dIII fragment carrying *actP* and *hmrR*:CAS-GNm (inactivation of the *hmrR Bcl*I site); Tc^{r}, Km^{r} | This study |

pRK2013 | Helper plasmid; Km^{r} | Figurski and Helinski (1979) |

pRT327 | RT3-27 *Eco*RI fragment containing Tn*5* cloned in pBR322; Ap^{r}, Km^{r} | This study |

pRT327-1 | Complementing plasmid clone from WSM419 genomic library; Tc^{r} | This study |

pSW213 | Broad host range cloning vector; Tc^{r} | Chen and Winans (1991) |

pTn*5*-H | *Hin*dIII fragment containing *nptII* from Tn*5* in pUC18; Ap^{r}, Km^{r} | This study |

pWR053 | *Hin*dIII fragment of pWR114 containing right inverted repeat of Tn*5* and associated rhizobial flanking sequence in pBR322; Ap^{r} | This study |

pWR114 | Tn*5*-containing *Eco*RI fragment of WR1-14 in pBR322; Ap^{r}, Km^{r}, Tc^{r} | This study |

pWR114L–Hp/E | *Hpa*I–*Eco*RI fragment containing a portion of Tn*5* IS50L and associated rhizobial DNA from pWR1-14 in pGEM-7Zf(+); Ap^{r} | This study |

pWR327-200 | Tn*5*-containing *Eco*RI fragment from RT3-27 in pJQ200SK; Gm^{r}, Km^{r} | This study |

pWR657 | *Not*I fragment containing CAS-GNm cloned from pCRS487 into the *Not*I site of pWR053; Ap^{r}, Km^{r} | This study |

pWR668 | *Hin*dIII–*Eco*RI blunted fragment containing the *actP*–*gusA* fusion from pWR657 in a blunted *Xho*I site of pCRS433; Tc^{r}, Km^{r} | This study |

pWR873 | *Eco*RI fragment containing Tn*5* from WR1-14 in pBRO1; Tc^{r}, Km^{r} | This study |

pWR880 | pWR873 devoid of Tn*5*; Tc^{r} | This study |

pWR901 | pWR880 derivative containing *actP* and *hmrR*:CAS-Gm (inactivation of the *hmrR Sph*I site); Tc^{r}, Gm^{r} | This study |

pWR903 | pWR880 derivative containing *actP* and *hmrR*:CAS-Gm (inactivation of the hmrR SphI site); Tc^{r}, Gm^{r} | This study |

pWR1033 | *Not*I fragment containing CAS-Gm cloned from pWR901 into *Not*I pJQ2ΩS; Suc^{s}, Gm^{r}, Sm^{r}, Sp^{r} | This study |

pWR1037 | *Not*I fragment containing CAS-Gm cloned from pWR903 into NotI pJQ2ΩS; Suc^{s}, Gm^{r}, Sm^{r}, Sp^{r} | This study |

**Phage** |

RL38 | Generalized transducing phage | Buchanan-Wollaston (1979) |