View source for General Information/ IS derivatives of Tn3 family transposons

'''<big>A</big>'''nother source of ambiguity for classification purposes occurs in the Tn''3'' family (see section “[[Transposons families|Tn families]]” and "[[Transposons families/Tn3 family|Tn''3'' family]]") [[:Image:1.15.1.png|(Fig.1.15.1]] and [[:Image:1.15.1.png| 1.15.2)]]. Tn''3'' family members are quite variable. They include a number of diverse passenger genes that can represent entire operons, notably mercury resistance, or individual genes involved in antibiotic resistance, breakdown of halogenated aromatics, or virulence [e.g. <ref><nowiki><pubmed>10477306</pubmed></nowiki></ref>]]. They often carry integron recombination platforms enabling them to incorporate additional resistance genes by recruiting integron cassettes. Members are quite characteristic: they have long relatively well conserved IR and a particularly long Tpase (950 to 1025 aa). They also encode a site-specific recombination (“resolution”) system necessary for completion of their transposition ([https://www.asmscience.org/content/book/10.1128/9781555817954.chap14 Grindley 2002] - Chapter 14 from [https://www.asmscience.org/content/book/10.1128/9781555817954 Mobile DNA II] book). There are a number of different resolution systems associated with different members of this family [[:Image:1.15.2.png|(Fig.1.15.2)]] IS''1071'', [[:Image:1.15.1.png|(Fig.1.15.1)]] composed of Tn''3''-like IR and Tpase gene but lacking both the site-specific recombination system and passenger genes was identified many years ago<ref><nowiki><pubmed>1656436</pubmed></nowiki></ref><ref><nowiki><pubmed>8117095</pubmed></nowiki></ref>. This clearly accords with the definition of an IS. Several other examples have now been identified (e.g. IS''Vsa19'', IS''Shfr9'', IS''Busp1'').
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|[[Image:1.15.1.png|thumb|center|510x510px|'''Fig. 1.15.1.''' Tn''3'' family characteristics.<br />Transposons are shown as yellow boxes with their names on the left and their lengths on the right. Terminal inverted repeats are shown as black arrowheads within the box.  Transposition-related genes (transposases and resolvase recombinases are shown as purple arrows), passenger genes as red arrows, for antibiotic resistance orange/yellow arrows for heavy metal resistance, bright yellow for plant pathenogenicity genes orange for toxin/antitoxin genes and blue for integron integrase genes. Resolution sites are shown in green.

Note that Tn''1071'' carries only a transposase gene and therefore could be considered an Insertion sequence.|alt=|border]]
|[[Image:1.15.2.png|thumb|center|510x510px|'''Fig. 1.15.2.''' Tn''3'' family resolvase configuration.

A) Tn''3'' has divergent transposase and resolvase (serine recombinase) genes with a res (resolution, recombination site between the divergent genes. It includes 3 sites at which resolvase binds (I, II and III).

B) Tn''501'' carries co-linear transposase and resolvase genes with the res site upstream of the resolvase.

C) Tn''4430'' has a similar configuration as Tn501 but its resolvase is a tyrosine recombinase and its res site, upstream of the resolvase has a more complex structure

D) TnXax1 carries two divergent genes, tnpS (a serine recombinase) and tnpT (a helper gene). The resolution site lies between the two genes and has a complex structure. |alt=]]
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==Bibliography==
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