This website has been set up to designate Tn numbers to researchers publishing details of new transposable elements discovered in bacteria and archaea. Transposable elements are defined as “specific DNA segments that can repeatedly insert into one or more sites in one or more genomes” (Roberts et al., 2008). This definition is modified from that stated in the original nomenclature proposal (Campbell et al., 1979a; 1979b) allowing it to include the many different types of transposable elements discovered since the original proposal was published.

New individual Tn numbers should be given to elements showing < 100% deduced nucleotide sequence similarity to their closest relatives, or to elements that contain novel resistance, virulence, catabolic or other accessory genes, or novel combinations of genes or modules. If functionality is demonstrated (excision, insertion, transposition or transfer) but the entire sequence of the element is not determined the element may still be assigned a Tn number provided the known sequence is sufficiently different from previously determined sequences, as described above. The rules governing the requesting of Tn numbers are summarised in a key below.

It is appreciated that other elements such as integrated or transposable prophage and satellite prophage, group I and II introns, IStrons, inteins, and insertion sequences fit this definition of a transposable element. However, in most cases there is already a coherent nomenclature system in place and any change would cause confusion. If a novel element is found which fails to qualify for an established nomenclature scheme a Tn number should be used.

Key for determining if a Tn number is appropriate. (not appropriate for ISs or non autonomous transposable elements such as integron cassettes or MITEs) (Roberts et al., 2008).

  1. Has excision, insertion, transposition and / or transfer been demonstrated?
    Yes; go to 3
    No; go to 2
  2. Has the entire DNA sequence been determined and the putative ends delineated?a
    Yes; go to 4
    No; go to 6
  3. Is any part of the DNA sequence of the element known?
    Yes; go to 4
    No; go to 6
  4. Is the nucleotide sequence <100% identical to known sequences?
    Yes; go to 7
    No; go to 5
  5. Is synteny conserved over the entire sequence compared to database sequences?
    Yes; got to 6
    No; got to 7
  6. A Tn number is inappropriate at this stage
  7. A Tn number is appropriate

ain the case of composite transposon flanked by IS elements transposition or different insertion sites need to be demonstrated, as it is possible that the majority of these have never transposed.

Roberts AP, Chandler M, Courvalin P, Guédon G, Mullany P, Pembroke T, Rood JI, Smith CJ, Summers AO, Tsuda M, Berg DE. (2008) Revised Nomenclature for Transposable Genetic ElementsPlasmid. 60; 167-173.

Campbell A, Starlinger P, Berg DE, Botstein D, Lederberg EM, Novick RP, Szybalski W. 1979. Nomenclature of transposable elements in prokaryotes. Plasmid. 2:466-73 andGene 5:197-206