TABLE 1.

Viability of exonuclease-deficient cells lacking RecG, RuvABC, RecA, Rep, UvrD, or RNaseHI

	Colony formation by plasmid-free segregants of synthetic lethality constructsa
Other chromosomal mutation(s)b	pAM401 sbcCD+/c	pJJ100 recG+/ΔrecG	pAM390 ruv+/Δruv	pAM490 rnhA+/ΔrnhA
None, or any 1 or 2 of xonA, xseA, sbcCD, recJ	+	+	+	+
xonA xseA recJ	+	+	*	−
xonA sbcCD recJ	+	+	+	+
xseA sbcCD recJ	+	+	+	+
xonA xseA sbcCD	+	−	−	−
rep or uvrD plus any 1 or 2 of xonA, xseA, sbcCD	+
xonA xseA sbcCD recQ	+
xonA xseA sbcCD helD	+
xonA xseA sbcCD dinG	+
xonA xseA sbcCD recF	*
priA300	+	+	+	+
xonA xseA sbcCD priA300	+	+	+d	−e

^aAs determined by using a synthetic lethality assay (materials and methods). +, plasmid-free segregants form well-developed colonies on LB agar equal to or approaching in size those formed by cells retaining the plasmid (unless indicated otherwise in the text). They also account for 25–75% of the total colonies observed and can be subcultured without difficulty. −, colonies of plasmid-free segregants not detected on either LB or 56/2 minimal salts agar, except as indicated in the text. *, plasmid-free segregants account for >20% of the total colonies observed on LB agar but establish colonies that are much smaller than those formed by cells retaining the plasmid; they establish much stronger colonies on 56/2 minimal salts agar and can be subcultured without difficulty under these conditions. See text for additional details.

^bThe mutations identified were deletions or in some cases (recA and recJ) Tn10 insertions (see Table S1), except for rus-2, which is an orf-56∷IS10 insertion activating rusA, and priA300, which is a base substitution encoding helicase-defective PriAK230R.

^cThe chromosome carries sbcCD⁺, except as indicated in column 1.

^dThe colonies formed on LB agar are smaller than those established by cells retaining the plasmid, but these two types of colonies are about equal in size on 56/2 minimal salts agar.

^eSmall colonies of plasmid-free segregants detected on 56/2 minimal salts agar, but could not be subcultured.