Table 5.

EOP ^a of λcI72 on host strains with immλ[TS] or hybrid imm plasmids ^b

Host strains	Plating temperature (˚C)
	25	30	35	37	39	42
594	0.5	0.9	0.9	1.0	1.0	0.4
594[pcIpR-P-timm]	<4 × 10-10	<4 × 10-10	0.2	0.5	0.7	1.0
594[pcIpR-O-timm]	<4 × 10-10	<4 × 10-10	<4 × 10-10	9 × 10-7c	2 × 10-6c	0.8
594[p434’pR-O-timm]	0.8	0.9	1.0	1.0	1.0	1.0

^a: EOP (efficiency of plating) of 1.0 determined for λimmλcI72 on host 594 at 37 ˚C.

^b: The CI[Ts] repressor made from the pcIpR plasmids blocks the vegetative growth of an infecting immλ phage as λcI72, at or below ~39 ˚C, as well as the expression of genes O or P, inserted downstream of the pR promoter. Plasmid p434’pR-O-timm has a hybrid cI gene fusion made from λ and 434 cI genes and the resulting repressor does not repress transcription from pR, allowing constitutive O expression at all temperatures [36].

^c: Rare min plaques can only be seen under stereo microscope.