In. Okeke et al., Comparative sequence analysis of the plasmid-encoded regulator of enteropathogenic Escherichia coli strains, INFEC IMMUN, 69(9), 2001, pp. 5553-5564
Enteropathogenic Escherichia coli (EPEC) strains that carry the EPEC adhere
nce factor (EAF) plasmid were screened for the presence of different EAF se
quences, including those of the plasmid-encoded regulator (per). Considerab
le variation in gene content of EAF plasmids from different strains was see
n. However, bfpA, the gene encoding the structural subunit for the bundle-f
orming pilus, bundlin, and per genes were found in 96.8% of strains. Sequen
ce analysis of the per operon and its promoter region from 15 representativ
e strains revealed that it is highly conserved. Most of the variation occur
s in the 5' two-thirds of the perA gene. In contrast, the C-terminal portio
n of the predicted PerA protein that contains the DNA-binding helix-turn-he
lix motif is 100% conserved in all strains that possess a full-length gene.
In a minority of strains including the O119:H2 and canine isolates and in
a subset of O128:H2 and O142:H6 strains, frameshift mutations in perA leadi
ng to premature truncation and consequent inactivation of the gene were ide
ntified. Cloned perA, -B, and -C genes from these strains, unlike those fro
m strains with a functional operon, failed to activate the LEE] operon and
bfpA transcriptional fusions or to complement a per mutant in reference str
ain E2348/69. Furthermore, O119, O128, and canine strains that carry inacti
ve per operons were deficient in virulence protein expression. The context
in which the perABC operon occurs on the EAF plasmid varies. The sequence u
pstream of the per promoter region in EPEC reference strains E2348/69 and B
171-8 was present in strains belonging to most serogroups. In a subset of O
119:H2, O128:H2, and O142:H6 strains and in the canine isolate, this sequen
ce was replaced by an IS1294-homologous sequence.