Figure 1.

Diagram of the pSymA megaplasmid in Sinorhizobium (Rhizobium) meliloti, illustrating the physical relationships among genes of the selenocysteine utilization system (selA, selB, selC and selD) and the only known selenoprotein gene in this organism, the α-subunit of formate dehydrogenase (fdhA). Also noted is the location of a putative transposon between selA/B and selC/D [11].