title: Second-element turn-on of gene expression in an IS1 insertion mutant.
abstract: To learn more about the ways in which genes silenced by insertion mutations can be reactivated, we have undertaken a systematic investigation of Gal+ revertants of the polar mutant galOP-306::IS1 in Escherichia coli K12. The selective conditions used excluded reversion to wild type by precise excision of IS1. In this system (which resided on a multi-copy plasmid) reversion to the Gal+ phenotype occurred with a frequency of about 10(-7) per cell and per generation. Analysis of the revertants revealed that - with the single exception of the previously published chromosomal mutant sis1 - alterations in the structure of IS1 lead to reactivation of gal operon expression. These events fall into four classes: (I) insertion of IS2 at position 327 in IS1, insertion of IS2 at position 687 in IS1, (III) insertion of a hitherto undetected mobile element, IS150, at position 387, (IV) a 16-bp deletion encompassing IS1 coordinates 553-568. Of some 200 independent reversion events studied, all but one were of types I-III i.e. they involved the intervention of a second mobile element.
authors.affiliation: Institut für Biologie III, Universität Freiburg, Federal Republic of Germany.
authors.forename: E
authors.initials: E
authors.lastname: Schwartz
authors.forename: C
authors.initials: C
authors.lastname: Herberger
authors.forename: B
authors.initials: B
authors.lastname: Rak
mesh_terms: D001483:Base Sequence; D004262:DNA Restriction Enzymes; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics*; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids
chemical_list: D004251:DNA Transposable Elements; D004262:DNA Restriction Enzymes