A genetic element that allows the positive selection of different genomic rearrangements was used to analyze DNA amplification in Rhizobium leguminosarum biovar phaseoli. Discrete amplifiable DNA regions (amplicons) were detected in different regions of the genome of the model strain CFN42, including the chromosome and several large plasmids. Amplicons were mobilized into Escherichia coli using a genetic approach that involves the introduction of an origin of replication active in E. coli and an origin of conjugal transfer into the amplifiable DNA regions of the Rhizobium genome. The strategy can be a valuable tool for studies on genome organization and function. We propose that amplicons define a structural characteristic of the genome that may play an important biological role.