The transfer origin for Bacteroides mobilizable transposon Tn4555 is related to a plasmid family from gram-positive bacteria

Conjugal transfer of Bacteroides mobilizable transposon Tn4555 was examined with an Escherichia coli-based assay system. It was shown that mobilization required the cis-acting oriT(9n) region and that the Tn4555 mob(Tn) gene and RK231 must be present in trans. With alkaline agarose gel electrophoresis and filter blot hybridizations, it was shown that at oriT(Tn) there was a site-and strand-specific cleavage event that was dependent on mobA(Tn). The 5' end of this cleavage site was mapped by primer extensin, and the nucleotide sequence surrounding the site had homology to a family of oriT nick sites found in mobilizable plasmids of gram-positive bacteria. Removal of the nick site by deletion of 18 bp surrounding the site resulted in a significant loss of transfer activity.