title: Vector insertion mutagenesis of Rhizobium sp. strain ORS571: direct cloning of mutagenized DNA sequences.
abstract: When the limited-host-range plasmid pVP2021 carrying Tn5 was mobilized into Rhizobium sp. strain ORS571 and stable acquisition of Tn5 was selected, ORS571 plasmid-genome cointegrates were exclusively obtained; direct Tn5 transposition was never observed. In every case, genomic cointegrates exhibited an additional (third) IS50 element that bordered VP2021 DNA sequences but maintained a single Tn5 element. Genomic cointegrates containing IS50 triplications were stable; neither phenotypic reversion nor resolution was detectable. Auxotrophic mutant strains (vector insertion mutants) were identified at expected frequencies among derivatives carrying ostensibly random genomic pVP2021 insertions; N2 fixation (Nif)-defective vector insertion mutants were observed among these derivatives at a frequency of 10(-3). The presence of integrated pVP2021 in ORS571 nif::VP2021 mutant genomes enabled VP2021 to constitute an endogenous cloning vector. After EcoRI or KpnI digestions, genomic nif::pVP2021 DNA sequences contiguous with integrated pVP2021 were directly cloned as new replicons without addition of an exogenous vector. Recombinant plasmids derived from two such nif::pVP2021 mutants hybridized to previously analyzed ORS571 Nif DNA sequences. Recombinant plasmid DNA and ORS571 Nif region DNA were found to be colinear; pVP2021 insertions could be accurately mapped. pVP2021 insertion-mutagenesis thus allows the direct cloning of ORS571 gene sequences for which mutant phenotypes can be selected or screened.
authors.forename: R G
authors.initials: RG
authors.lastname: Donald
authors.forename: C K
authors.initials: CK
authors.lastname: Raymond
authors.forename: R A
authors.initials: RA
authors.lastname: Ludwig
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005822:Genetic Vectors; D009154:Mutation; D010957:Plasmids; D012231:Rhizobium / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements