Characterization of a small mobilizable transposon, MTnSag1, in Streptococcus agalactiae

Abstract

The transposon MTnSag1 from Streptococcus agalactiae carried an IS1-like transposase gene and the lnu(C) gene, which encoded a lincosamide nucleotidyltransferase. MTnSag1 could be mobilized by the conjugative transposon Tn916. An intermediate circular form of MTnSag1 and a putative origin of transfer at the 3' end of the lnu(C) gene were characterized.

FIG. 1.

Sequence alignment of N termini of MTnSag1 and IS1 transposases. Putative ZF and helix-turn-helix (HTH) motifs are shown. Conserved C residues forming a putative ZF motif are underlined; a conserved aromatic residue is in bold, and the helix-turn-helix motif is boxed. The insertion sequence elements described can be found in ISfinder (http//:www-IS.biotoul.fr); the accession number of MTnSag1 in the GenBank data library is AY928180.

FIG. 2.

MTnSag1 oriT mobilization assays. (A) Schematic map of MTnSag1. Inverted repeats (IR) are indicated by dotted lines. (B) Cloned fragments for MTnSag1 oriT mobilization. The sizes of the fragments and the corresponding plasmid designations are indicated. The frequency of mobilization was determined by dividing the number of transconjugants that received the mobilized plasmid by the number of donor cells. Values are means of a minimum of three independent mating experiments.

FIG. 3.

Sequence analysis of the putative MTnSag1 origin of transfer. (A) Comparison of the Int-protected region of oriT from Tn916 with the MTnSag1 sequence. Upper line: nucleotides 1575 to 1635 of MTnSag1. Lower line: protected oriT sequence from Tn916. Vertical dots indicate bases in the transposon that are identical to bases of the Int-protected region. (B) Map of the putative oriT_1488-1667 of MTnSag1. The putative Int binding site is indicated by a dashed line above the sequence. Inverted arrow pairs indicate inverted repeat structures.