Florfenicol-chloramphenicol exporter gene fexA is part of the novel transposon Tn558

Abstract

The florfenicol-chloramphenicol exporter gene fexA is part of the novel transposon Tn558 from Staphylococcus lentus. Similarities between Tn558 and Tn554 from Staphylococcus aureus included the arrangement of the transposase genes tnpA to -C and an att554-like target sequence. Circular forms of Tn558 were detected and suggest the functional activity of this transposon.

FIG.1.

(A) Organization of the S. lentus transposon Tn558 in comparison to the structurally related transposons Tn554 (X03216) and Tn5406 (AF186237). A distance scale in kilobases is given below each map. The position and orientation of the genes coding for transposition functions (tnpA, tnpB, and tnpC), antimicrobial resistance [vga(A), streptogramin A resistance; erm(A), resistance to macrolides, lincosamides, and streptogramin B antibiotics; spc, spectinomycin resistance; fexA, resistance to florfenicol and chloramphenicol], or unknown functions (orf, orf138) are indicated by arrows with the direction of transcription shown by the arrowhead. The restriction endonuclease cleavage sites are abbreviated as follows: B, BclI; Bg, BglII; C, ClaI; E, EcoRI; K, KpnI; P, PstI; Pv, PvuII; X, XhoI. The positions of primers used for the detection of circular Tn554 forms are labeled circ-fw and circ-rev and are indicated by arrows. The 6-bp core nucleotide sequences at the transposon junctions are shown in boxes. (B) Nucleotide and amino acid sequence alignment of the attachment sites att554 (in S. aureus N315 [3) and att155 (in S. epidermidis [13]) of Tn554, that of Tn5406 in S. aureus strain BM3252 (3), and att558 of Tn558 in plasmid pSCFS2. An attachment site identical to att554 has also been reported for Tn5406 in S. aureus strain BM3327 (3). Grey boxes indicate identical amino acids found in three or more of the aligned sequences. The hexanucleotide core sequences of the integration sites are framed. The black bar above the att554 sequence indicates the minimum sequence required for transposition into this site as determined by deletion analysis (5, 6).