Studies on IS DNA
IS-elements are unique, transposable DNA sequences lacking a trans-acting phenotype. They are detectable by the effects they exert in the cis position on adjacent genes at sites to which they are transposed by a rare illegitimate recombination event. These effects include mutation (of a gene, into which the IS-element is integrated), polar effects (of genes located distal to the IS-element, but in the same transcription unit), initiation of transcription of a silent gene (if an IS-element carrying a promoter is integrated in front of a gene that has lost its own promoter) and an increase in the frequency of a variety of chromosomal aberrations occurring in the vicinity of IS-elements. IS-elements play a role in the integration of plasmids into chromosomes (e.g. in the formation of Hfr strains by the integration of the F-plasmid) and some of them have been identified as part of transposons (= transposable DNA sequences carrying one or more genes, most of them coding for resistance to an antibiotic, and usually bordered by a DNA sequence, repeated at the end of the transposon directly or in inverted form). This repeated sequence has been identified as an IS-element in some cases. The properties of IS-elements have been reviewed in more detail elsewhere (1,2,3,4).
KeywordsIntegration Site Leader Sequence Elongation Reaction Inverted Form Heteroduplex Molecule
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