Independent invasion of ISRm10-2 copies by RmInt1. (A) Ethidium bromide-stained agarose gel of amplified fragments of the intergenic region between nodJ and nodQ1, from total DNA of the cluster II isolates and the control strain 1021 (see Materials and Methods). Various amplified fragments were obtained: 1,614 a, 3,971 b and 5,855 c bp. (B) Structure of each amplified fragment. White boxes indicate genes present on pSymA in 1021 and the C3 isolate; gray boxes indicate the acquisition of IS transposable elements in the B1, B9, B10 and C10 isolates and the black box indicates the insertion of the RmInt1 group II intron into ISRm10-2 in isolate C4. Arrowheads indicate the positions of the primers used.