TABLE 1.

E. coli strains and plasmids

Strain or plasmid	Relevant genotype	Reference or source
Strains
DM49	lexA3	29
FC526	ΔrecG263::kan	11
GY8322	Δ(srlR-recA)306::Tn10	S. Sommer; ENZ280 (8) carrying the K5353 mini-F plasmid (9)
SMR821	lexA3 malB::Tn9	33
SMR1827	FC40 sulA211	33
SMR4562^a	rec⁺attλ⁺	33; genotype identical to FC40 (4)
SMR4649	FC40 sulA211 lexA51	33
SMR5078	recB21 recC22 sbcB15 sbcC201 hsdr_K⁻m_K⁺ (λxis1 cIts857)	14
SMR5156	SMR4562 (λxis1 cIts857)	SMR4562 × λSR446 (14)
SMR5201	recB21 recC22 sbcB15 sbcC201 hsdrK⁻mK⁺ Δattλ::ampRC	SMR5078 × DNA from pJP2
SMR5222	SMR4562 Δattλ::ampRC	SMR 5156 × P1 SMR5201
SMR5225	SMR5222 Δ(srlR-recA)306::Tn10	SMR5222 × P1 GY8322
SMR5578	SMR5222 ΔrecG263::kan	SMR5222 × P1 FC526
SMR5652	SMR5222 ΔrecG263::kan Δ(srlR-recA)306::Tn10	SMR5578 × P1 GY8322
SMR5701	SMR1827 (λxis1 cIts857)	SMR1827 × λSR446
SMR5702	SMR4649 (λxis1 cIts857)	SMR4649 × λSR446
SMR5715	SMR5222 lexA3 malB::Tn9	SMR5222 × P1 SMR821
SMR5725	SMR5222 sulA211 lexA51	SMR5702 × P1 SMR5201
SMR5749	SMR5222 sulA211	SMR5701 × P1 SMR5201
Plasmids
pEc1c	E. cloacae ampRC⁺	35
pJP2	pTGV-light ampRC⁺	This work
pJP19	pACYC184 ampD⁺	This work^b

↵a Full genotype is Δ(lac-pro)XIII thi ara Rif^r [F′ α45, lacI^q lacI33ΩlacZ].
↵b Plasmid pJP19, carrying the E. coli ampD⁺ gene and promoter, was created by amplifying ampD⁺ from E. coli wild-type strain MG1655 (3) chromosomal DNA using primers AmpD no. 1, 5′-GGGTTTTCATGAGAGGCGGCATGTTAAAACTCCAG-3′; and AmpD no. 2, 5′-GGGTTTAAGCTTTCATGTTGTCTCCTTGCTGACCAG-3′. The primers incorporate terminal BspHI and HindIII restriction sites at the 5′ and 3′ ends (respectively) of the amplified fragment. Amplified ampD⁺ DNA and pACYC184 DNA (5) were digested with BspHI and HindIII, and the ampD⁺ fragment was ligated into pACYC184. pJP19-mediated ampD expression was confirmed by complementation to β-lactam sensitivity of four independent ampD β-lactam-resistant mutants.