<jats:title>ABSTRACT</jats:title> <jats:p> Streptomycetes are common soil inhabitants, yet few described species are plant pathogens. While the pathogenicity mechanisms remain unclear, previous work identified a gene, <jats:italic>nec1</jats:italic> , which encodes a putative pathogenicity or virulence factor. <jats:italic>nec1</jats:italic> and a neighboring transposase pseudogene, ORF <jats:italic>tnp</jats:italic> , are conserved among unrelated plant pathogens and absent from nonpathogens. The atypical GC content of <jats:italic>nec1</jats:italic> suggests that it was acquired through horizontal transfer events. Our investigation of the genetic organization of regions adjacent to the 3′ end of <jats:italic>nec1</jats:italic> in <jats:italic>Streptomyces scabies</jats:italic> 84.34 identified a new insertion sequence (IS) element, IS <jats:italic>1629</jats:italic> , with homology to other IS elements from prokaryotic animal pathogens. IS <jats:italic>1629</jats:italic> is 1,462 bp with 26-bp terminal inverted repeats and encodes a putative 431-amino-acid (aa) transposase. Transposition of IS <jats:italic>1629</jats:italic> generates a 10-bp target site duplication. A 77-nucleotide (nt) sequence encompassing the start codon and upstream region of the transposase was identified which could function in the posttranscritpional regulation of transposase synthesis. A functional copy of IS <jats:italic>1629</jats:italic> from <jats:italic>S. turgidiscabies</jats:italic> 94.09 (Hi-C-13) was selected in the transposon trap pCZA126, through its insertion into the λ <jats:italic>cI</jats:italic> 857 repressor. IS <jats:italic>1629</jats:italic> is present in multiple copies in some <jats:italic>S. scabies</jats:italic> strains and is present in all <jats:italic>S. acidiscabies</jats:italic> and <jats:italic>S. turgidiscabies</jats:italic> strains examined. A second copy of IS <jats:italic>1629</jats:italic> was identified between ORF <jats:italic>tnp</jats:italic> and <jats:italic>nec1</jats:italic> in <jats:italic>S. acidiscabies</jats:italic> strains. The diversity of IS <jats:italic>1629</jats:italic> hybridization profiles was greatest within <jats:italic>S. scabies</jats:italic> . IS <jats:italic>1629</jats:italic> was absent from the 27 nonpathogenic <jats:italic>Streptomyces</jats:italic> strains tested. The genetic organization and nucleotide sequence of the <jats:italic>nec1</jats:italic> -IS <jats:italic>1629</jats:italic> region was conserved and identical among representatives of <jats:italic>S. acidiscabies</jats:italic> and <jats:italic>S. turgidiscabies</jats:italic> . These findings support our current model for the unidirectional transfer of the ORF <jats:italic>tnp-nec1</jats:italic> -IS <jats:italic>1629</jats:italic> locus from IS <jats:italic>1629</jats:italic> -containing <jats:italic>S. scabies</jats:italic> (type II) to <jats:italic>S. acidiscabies</jats:italic> and <jats:italic>S. turgidiscabies</jats:italic> .