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| ===Original Identification===
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| '''<big>T</big>'''he founding member [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISLr2 IS''Lr2''] was identified in [[wikipedia:Lactobacillus_delbrueckii_subsp._bulgaricus|''Lactobacillus delbrueckii'' subsp. ''Bulgaricus'']]<ref><pubmed>7565604</pubmed></ref> a bacterium used mainly for production of yogurt in mixed-strain thermophilic culture together with [[wikipedia:Streptococcus_thermophilus|''Streptococcus thermophilu''s]] where is being responsible for the loss of the capacity to ferment lactose. It was noted to be similar to [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1165 IS''1165''] from [[wikipedia:Leuconostoc_mesenteroides|''Leuconostoc mesenteroides'' subsp. ''cremoris'']] strain DB1165 also used in commercial mesophyllic starter cultures<ref><pubmed>:1325060</pubmed></ref>.<ref><nowiki>{{#pmid:1325060}}</nowiki></ref>
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| ===Distribution===
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| There are more than 150 members from nearly 80 bacterial species. The family also includes archaeal members, particularly in the [[wikipedia:Methanomicrobia|Methanomicrobia]].
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| Potential tIS derivatives with passenger genes appear quite common. These include a [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3466566/ mercury resistance operon]<ref name=":0"><pubmed>15907536</pubmed>
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| </ref> in Tnmer1 ([https://www.ncbi.nlm.nih.gov/nuccore/AY351675.1/ AY351675]) from a conjugative plasmid, pPPM1000, in ''[[wikipedia:Enterococcus_faecium|Enterococcus faecium]]'' and in [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISStma11 IS''Stma11''] from ''[[wikipedia:Stenotrophomonas_maltophilia|Stenotrophomonas maltophilia]]'' ([https://www.ncbi.nlm.nih.gov/nuccore/NC_010943 NC_010943]). A number of other '''tIS''' derivatives with additional types of passenger gene such as restriction modification systems in ''[[wikipedia:Acinetobacter_bereziniae|Acinetobacter bereziniae]]'' ([https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISAbe14 IS''Abe14'']; [https://www.ncbi.nlm.nih.gov/nuccore/LKDJ00000000.2 LKDJ01000006]), ''[[wikipedia:Serratia_marcescens|Seratia marcesens]]'' ([https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISSm1 IS''Sm1'']) ''[[wikipedia:Klebsiella_pneumoniae|Klebsiella pneumoniae]]'' ([https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISKpn25 IS''Kpn25'']; [https://www.ncbi.nlm.nih.gov/nuccore/NC_009650.1/ NC_009650]) have also been identified. There are several additional examples of this type of structure: [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] (''[[wikipedia:Pseudomonas_putida|Pseudomonas putida]]''; [https://www.ncbi.nlm.nih.gov/nuccore/AY128707 AY128707]); [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPst2 IS''Pst2''] (''[[wikipedia:Pseudomonas_stutzeri|Pseudomonas stutzeri]]'' ; [https://www.ncbi.nlm.nih.gov/nuccore/AJ012352 AJ012352]); [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISEc53 IS''Ec53''] (''[[wikipedia:Escherichia_coli|Escherichia coli]]''; [https://www.ncbi.nlm.nih.gov/nuccore/HG941718 HG941718]); [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISRso21 IS''Rso21''] (''[[wikipedia:Ralstonia_solanacearum|Ralstonia solanacearam]]'').
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| [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1167 IS''1167''] copies have been found flanking the ''cap1'' (capsular polysaccharide) locus of type 1 ''[[wikipedia:Streptococcus_pneumoniae|S. pneumoniae]]'' forming a potential compound transposon<ref><pubmed>11902728</pubmed></ref>. It has also used as a tool to distinguish between ''[[wikipedia:Streptococcus_pneumoniae|S. pneumoniae]]'' strains<ref><pubmed>9878026</pubmed></ref> using [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1167 IS''1167''] [[wikipedia:Restriction_fragment_length_polymorphism|'''R'''estriction '''F'''ragment '''L'''ength '''P'''olymorphism (RFLP)]] pattern analysis<ref><pubmed>10747146</pubmed></ref>. The ''[[wikipedia:Pseudomonas_putida|Pseudomonas putida]]'', [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1411 IS''1411''], was discovered by its ability to insertional activate promoter less ''pheBA'' genes by insertion due to an outward-directed promoter(s) at its left end<ref name=":1"><pubmed>9765560</pubmed>
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| </ref>.
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| Small sequences (130-340 bp) related to the [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1167 IS''1167''] '''IRs''' have been detected in ''[[wikipedia:Streptococcus_sanguinis|Streptococcus sanguis]]'', ''[[wikipedia:Streptococcus_pneumoniae|S. pneumoniae]]'', and ''[[wikipedia:Streptococcus_agalactiae|S. agalactiae]]''<ref><pubmed>2352474</pubmed></ref><ref><pubmed>7597107</pubmed></ref>.
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| ===Organization===
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| Members range in size from 1186 bp to 1553 bp, carry closely related IR of between 15 and 39 bp [[:File:Fig. ISL3.1.png|(Fig.IS''L3'')]] and generate DR of 8 bp. They generally have a single orf of between 400 and 440 amino acids which shows good alignment and includes an α-helical insertion domain<ref><pubmed>20067338</pubmed></ref>.
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| [[Image:Fig. ISL3.1.png|thumb|center|620x620px|'''Fig. IS''L3''.''' '''General IS''L3'' characteristics, average length, and common ends. Top:''' Distribution of IS length (base pairs) of IS''L3'' family members. The number of examples used in the sample is shown above each column. '''Bottom''': Left ('''IRL''') and right '''IRR''' inverted terminal repeats are shown in [http://weblogo.threeplusone.com/ WebLogo] format.|alt=]]
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| While most carry only a single orf, the transposase, several variants include additional orfs: [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1096 IS''1096''] harbors two orfs: the upstream orf exhibits similarities to the IS''L3'' family Tpases; the second, ''tnpR'', a [https://www.ncbi.nlm.nih.gov/pubmed/12829265 MerR-like transcription factor], is related to orfs from ''[[wikipedia:Rhizobium_rhizogenes|Agrobacterium rhizogenes]]'' and ''[[wikipedia:Rhizobium|Rhizobium]]'' sp. plasmids. TnpR appears to regulate transposition activity of [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12'']<ref name=":2"><pubmed>20061472</pubmed>
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| </ref>; [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] in addition to a ''tnpA'' homologue carries three open reading frames, a PnbR-like regulatory protein of the [https://www.uniprot.org/uniprot/P0A183 MerR family], a putative membrane/transport protein and a putative [https://www.uniprot.org/uniprot/P00804 lipoprotein signal peptide-like protein (''lspA'')]<ref><pubmed>12426346</pubmed></ref><ref><pubmed>12426347</pubmed></ref>.
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| In [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1167 IS''1167''], the reading frame appears to be distributed between two consecutive orfs with a potential for translational coupling suggested by overlapping initiation and termination codons (ATGA).
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| ===Mechanism===
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| Transposition of most of these elements has been demonstrated, but no detailed analysis of their transposition mechanism has yet appeared. [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1411 IS''1411''] from ''[[wikipedia:Pseudomonas_putida|Pseudomonas putida]]'' forms a circular species with abutted IS ends separated by 5 bp from the DNA flank of one IS end <ref name=":1" />. Clearly, as is the case in other IS which form circular transposition intermediates, expression of the ''tnp'' gene will be driven by the leftward oriented promoter. Transposon circles are also formed by [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPst9 IS''Pst9'']<ref><pubmed>18645960</pubmed></ref> and the tIS, Tn''mer1'' <ref name=":0" /> and in both cases the abutted '''IRs''' are also separated by 5 bp. An isoform of [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12'']''<ref name=":2" />'', [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS31831 IS''31831''] and [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS1411 IS''1411'']''<ref name=":1" />'' forms DNA species with a size expected for an excised transposon circles. For [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=IS31831 IS''31831''], derivatives of which have been used in [[wikipedia:Mutagenesis|mutagenesis]], the majority of insertions were found to be simple and only rare clones carried accompanying vector DNA<ref><pubmed>8196545</pubmed></ref>.
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| There is some evidence indicating that transposition of these IS can be induced by a form of zygotic induction following conjugative transfer ''<ref name=":2" />'' although the phenomenon is not understood. [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPst9 IS''Pst9''] undergoes transposition in the resident ''[[wikipedia:Pseudomonas_stutzeri|Pseudomonas stutzeri]]'' strain when brought into contact with a conjugative ''[[wikipedia:Escherichia_coli|E. coli]]'' strain, ''[[wikipedia:Escherichia_coli|E. coli]]'' S17-1 lambda(pir), and undergoes deletion. Activation requires a second IS''L3'' derivative, [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''], in the same strain.
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| Although both IS''L3''-like ISs are similar, they differ in their accompanying genes: Mutation of TnpR, a [https://www.uniprot.org/uniprot/P0A183 MerR-like] transcriptional regulator present in [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] but not in [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPst9 IS''Pst9''], reduced the [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] ''tnpA'' transcription and decreased formation of transposon circle transposition intermediates after conjugative interaction. Complementation of TnpR restored the ability to activate transposition but the expression of TnpR in the absence of [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] did not result in conjugative induction of [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPst9 IS''Pst9'']. This suggests that [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] TnpR activates [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] ''tnpA'' transcription and raises the possibility that [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] TnpA might bind '''IRs''' of both [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPpu12 IS''Ppu12''] and [https://tncentral.ncc.unesp.br/ISfinder/scripts/ficheIS.php?name=ISPst9 IS''Pst9''] and catalyze transposition of both elements.
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| No obvious target sequence specificity has yet been observed, although there is some suggestion that there may be a preference for AT-rich regions.
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| <br />
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| ==Bibliography==
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| {{Reflist|32em}}
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| <br />
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| <hr>
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| {{TnPedia}}
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