TABLE 1.

Plasmids constructed in this study

Plasmid	Description
pKM116	The filled-in 6,732-bp BspHI fragment from pKM587, containing ptr, recB, and the proximal portion of recD, was ligated to the filled-in EcoRI site of pBR322, with recB reading clockwise, opposite to bla. The EcoRI sites are reconstructed following ligation.
pKM118	The EcoRI site near the recD sequences in pKM116 was removed by partial digestion of pKM116 with EcoRI, followed by treatment with Klenow fragment and dNTPs and religation.
pKM119	The XmaI (filled-in)-PstI fragment of pKM587, containing sequences upstream of recC, was ligated to the PstI-EcoRI (filled-in) fragment of pBR322. The EcoRI site is reconstructed following ligation.
pKM120	The 7,107-bp EcoRI-BamHI fragment from pKM118, containing sequences downstream of recC, was ligated to the 5,333-bp EcoRI-BamHI fragment from pKM119, containing sequences upstream of recC. The tetracycline resistance gene is reconstructed following ligation.
pKM121	The 1,100 bp PstI fragment from pJM22 containing kan was treated with T4 DNA polymerase and dNTPs and ligated into the filled-in EcoRI site of pKM120.
pKM123	The 1,908-bp BamHI-SspI fragment from pCDK3, containing the distal end of recD and downstream sequences, was ligated to the EcoRV-BamHI fragment of pBR322.
pKM124	The 1,100-bp PstI fragment from pJM22 containing kan was treated with T4 DNA polymerase and dNTPs and ligated to the filled-in HindIII site of pKM123. The kan gene is read counterclockwise, in the same direction as bla.
pKM125	The 5,710-bp EcoRI-BamHI fragment from pKM119, containing sequences upstream of recC and ori, was ligated to the 3,041-bp EcoRI-BamHI fragment from pKM124, containing the kanamycin resistance determinant and sequences downstream of recD.
pKM126	The 1,700-bp fragment containing the Plac-bet exo operon, generated by partial digestion of pTP232 with EcoRI, was ligated to the EcoRI site of pKM125. Both red and kan are transcribed counterclockwise, in the direction of sequences upstream of recC.
pKM130	The 2,500-bp PvuII fragment containing most of the lacZ sequence from pMV201 (M. Volkert) was ligated to the PvuII site of pBR322.
pKM131	The 1,100-bp PstI fragment from pJM22 containing kan was treated with T4 DNA polymerase and dNTPs and ligated to the filled-in BclI site of pKM130.
pKM132	pKM130 was digested with EcoRI and MscI, filled in with Klenow fragment and dNTPs, and religated.
pKM133	The filled-in EcoRI and MscI fragment from pKM130, containing the tetracycline resistance determinant, was ligated to the filled-in BclI site of pKM132.