FIG. 1.

(A) Map of Tn916 (18,032 bp). Identified open reading frames and the directions of their transcription are indicated by the arrows below the map. Areas that have been identified as important for specific functions are identified by open boxes below the map. For more detail on the left end of Tn916, refer to panel B. Points designated by the letters F, P, or Q, with or without numbers following them, represent sequences with homology to the nic sites of plasmid IncF, IncP, or IncQ, respectively. The region between open reading frames 20 and 21 allows nonconjugative plasmids to be mobilized by chromosomal copies of Tn916, and therefore represents a functional origin of transfer for Tn916. Adapted with permission from reference 27. (B) Schematic portrayal of the left end of Tn916. The terminus of the transposon is marked. The open reading frames (ORFs) are designated by names [xis-Tn, int-Tn, traA, tet(M)] if such designations have been given. Otherwise they are listed as numbered open reading frames. Arrows above or below the boxes represent the direction of transcription of the indicated gene. tet(M) confers tetracycline and minocycline resistance. Open reading frames 6, 9, and 10 have no identified function but appear to be related to the tet(M) gene since tet(M) transcripts of extended length (corresponding to the length added by these open reading frames) have been identified after tetracycline exposure. T-tetM indicates the terminator of the tet(M) transcript. T-3.2 indicates a potential termination site for the extended 3.2-kb transcript seen after tetracycline exposure (see text). Open reading frames 7 and 8 have no identified function. traA is thought to be a positive activator of conjugation functions, all of which are located on the opposite side of tet(M) within Tn916. int-Tn encodes the integrase that is responsible for transposition; xis-Tn encodes the excisase that increases the frequency of excision, but is not required.