Transposition intermediates called "transposomes" are complexes between two transposase mols. and any DNA with ME inverted repeat ends. The transposome formation from Tn5 transposable elements, different transposon insertion site localization methods, specialized transposon for mutagenesis of gene for exported or membrane peptide, transposome mutagenesis in organism without characterized genetic system, transposome insertion with phenotypic consequences, and signature-tagged mutagenesis applied to transposomes are described. Tn5 transposomes may be introduced into the chromosomes of many bacterial species by electroporation. The efficiency of insertion varies from organism to organism, but it is usually high enough to produce a library of knockout mutations. In addition, transposomes can be used to deliver genomic control elements, screen-able markers, or reporter genes whose activities can be measured under different metabolic states. With new transposition tools called transposomes, many barriers to the insertion of transposon into genomic DNA are removed. (c) 2002 Academic Press.