A family of stability determinants in pathogenic bacteria - PubMed (original) (raw)

A family of stability determinants in pathogenic bacteria

F Hayes. J Bacteriol. 1998 Dec.

Abstract

A novel segregational stability system was identified on plasmid R485, which originates from Morganella morganii. The system is composed of two overlapping genes, stbD and stbE, which potentially encode proteins of 83 and 93 amino acids, respectively. Homologs of the stbDE genes were identified on the enterotoxigenic plasmid P307 from Escherichia coli and on the chromosomes of Vibrio cholerae and Haemophilus influenzae biogroup aegyptius. The former two homologs also promote plasmid stability in E. coli. Furthermore, the stbDE genes share homology with components of the relBEF operon and with the dnaT gene of E. coli. The organization of the stbDE cassette is reminiscent of toxin-antitoxin stability cassettes.

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Figures

FIG. 1

FIG. 1

(A) Genetic organization of the stbDE genes and flanking regions from plasmid R485. Arrows indicate the length and orientation of open reading frames. Lines beneath the map indicate regions cloned in the stability probe vector, pALA136. The levels of retention conferred by these fragments after approximately 25 generations in the absence of selective pressure in a polA strain are shown. (B) Nucleotide sequence of the 1,154-bp _Sca_I-_Bgl_II fragment from plasmid R485. The inferred amino acid sequences of the four open reading frames are shown by the single-letter code.

FIG. 2

FIG. 2

(A) Comparative organizations of the stbDE genes from plasmid R485 and homologous genes from plasmid P307 and from the chromosomes of V. cholerae, E. coli, and H. influenzae biogroup aegyptius. Homologous regions are denoted by similar shadings. The asterisk indicates the position of the −1 frameshift in the stbE gene of H. influenzae biogroup aegyptius. (B) Homology between the RelB, DnaT, and putative StbD proteins. The DnaT and StbD proteins are aligned from their N termini, whereas the RelB and StbD proteins are aligned from their C termini. No gaps were introduced into the alignments. Shaded lines represent amino acids which are identical between proteins.

FIG. 3

FIG. 3

Homology in the StbD (A) and StbE (B) families of proteins. Residues which are identical in a majority of family members are shaded. Dashes indicate gaps introduced to optimize the alignments. Protein sequences were aligned with the PILEUP program (4) with subsequent manual modification. Note that for the StbE′ protein from H. influenzae biogroup aegyptius, a hypothetical +1 frameshift, indicated by an asterisk in the protein sequence, was introduced in the nucleotide sequence to maintain the integrity of the gene.

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