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, 58 (2), 1235-9

Nucleotide Sequence Analysis of Integrative Conjugative Element Tn5253 of Streptococcus Pneumoniae

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Nucleotide Sequence Analysis of Integrative Conjugative Element Tn5253 of Streptococcus Pneumoniae

Francesco Iannelli et al. Antimicrob Agents Chemother.

Abstract

Conjugative transposon Tn5253, an integrative conjugative element (ICE) of Streptococcus pneumoniae carrying the cat and tet(M) genes, was shown to be 64,528 bp in size and to contain 79 open reading frames, of which only 38 could be annotated. Two distinct genetic elements were found integrated into Tn5253: Tn5251 (18,033 bp), of the Tn916-Tn1545 family of ICEs, and Ωcat(pC194) (7,627 bp), which could not conjugate but was capable of intracellular mobility by excision, circularization, and integration by homologous recombination. The highest conjugation frequency of Tn5253 was observed when Streptococcus pyogenes was the donor (6.7 × 10(-3) transconjugants/donor).

Figures

FIG 1
FIG 1
Structure of S. pneumoniae Tn5253. Sequence analysis of Tn5253 showed that it is 64,528 bp in size and contains 79 ORFs. Tn5253 contains two distinct integrated genetic elements, the 18,033-bp-long ICE Tn5251 carrying tet(M) and the 7,627-bp-long element Ωcat(pC194) containing cat. ORFs and their directions of transcription are represented by arrows, and the annotated ORFs are indicated only by their numbers. The regions corresponding to Tn5251 and Ωcat(pC194) are indicated by solid bars, and their ORFs are represented by thinner arrows. Tetracycline and chloramphenicol resistance genes are represented by red arrows. Chromosomal genes flanking the Tn5253 insertion site are represented by thin gray arrows. The different GC contents of the various regions are indicated by dotted bars. Homologies with pneumococcal chromosomal regions are marked by solid lines. The scale is in kilobases.
FIG 2
FIG 2
S. pneumoniae Ωcat(pC194) is a 7,627-bp-long element integrated into Tn5253 and contains a copy of plasmid pC194 lacking its replication origin. It is flanked by two 1,169-bp DRs (boxed yellow arrows) that are part of two longer 1,357-bp imperfect DRs. The 5′ and 3′ ends of the imperfect DRs are represented by red (a and a′) and blue (b and b′) boxes. Ωcat(pC194) is excised from Tn5253 and produces a circular form and a deletion in Tn5253. Excision of Ωcat(pC194) occurs by recombination between the flanking DRs and leaves in Tn5253 a single DR flanked by a and b′, while the DR of the circular form is flanked by a′ and b.

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