Table 1. Ability of β^Cys to support E. coli viability.

Transforming plasmida	β-Clamp protein	Frequency of pAMPdnaN+ retentionb	E. coli viabilityc	β-Clamp expression levelsd	Doubling time (min)e
pACM	None (negative control)	20/20 (100%)	–	NA	NA
pACMdnaN+	eβWT (positive control)	2/20 (10%)	+	0.93 ± 0.08 (P = 0.26)	37 ± 1.5
pACMβCys	eβCys	2/20 (10%)	+	0.95 ± 0.13 (P = 0.56)	42 ± 2.1 (P = 0.03)

^aStrain MS201 bearing plasmid pAMPdnaN⁺ was transformed with the incompatible plasmids pACM, pACMdnaN⁺ or pACMβ^Cys, as indicated.

^bThe frequencies of pAMPdnaN⁺ retention in 20 randomly selected pACM, pACMdnaN⁺ or pACMβ^Cys transformants following ∼100 generations are indicated. Representative clones lacking pAMPdnaN⁺ were characterized further to verify they contained both the chromosomally-encoded dnaN^−1FS as well as the indicated plasmid-encoded dnaN allele.

^cViability refers to the ability of pACM, pACMdnaN⁺ or pACMβ^Cys to support growth of E. coli in the absence of pAMPdnaN⁺.

^dValues represent the average of triplicates ± one standard deviation, and are expressed relative to the level observed in the isogenic strain RW118. P values were calculated relative to the isogenic parent strain RW118 using the Student's t-test.

^eResults shown are the average of three independent determinations ± one standard deviation. The P value for the strain bearing pACMβ^Cys was calculated relative to the pACMdnaN⁺ strain using the Student's t-test.