TABLE 2.

Dam is essential for viability in Y. pseudotuberculosis and V. cholerae^a

Strain	Plasmid	No. of colonies with the indicated genotype at the dam locus after excision of pCVD442
		dam+	Δdam
Y. pseudotuberculosis
MT2357	None	200	0
MT2358	dam+ (Y. pseudotuberculosis)	135	44
MT2359	dam+ (E. coli)	151	21
MT2360	Vector alone	200	0
V. cholerae
MT2361	None	196	0
MT2362	dam+ (V. cholerae)	153	47
MT2363	dam+ (E. coli)	118	76
MT2364	Vector alone	194	0

^aIntegration of the suicide plasmid pCVD442 (8) into the Y. pseudotuberculosis or V. cholerae chromosome results in a duplication of the dam locus wherein one copy contains the wild-type dam gene and the other copy contains dam with a deletion associated with a kanamycin resistance marker (22). Selection for the excision of pCVD442 on plates containing 10% sucrose result in either dam⁺ or dam mutant (Δdam::Kn) segregants (8). The dam mutant segregants of Y. pseudotuberculosis or V. cholerae are associated with chromosomal internal deletions of 314 or 324 bp of the dam sequence, respectively. For plasmid complementation experiments, pWKS30-Tc (43) was used to provide the dam gene from Y. pseudotuberculosis, V. cholerae, or E. coli as indicated.