Fig 3. Synthesis of (c)mnm⁵s²U in bacteria.

Note that a mutations in mnmA, tusB or tusE block the formation of the s²-group and mutations in either mnmE or mnmG (gidA) block the synthesis of the side chain (c)mnm⁵-. In the bacterium Salmonella enterica Serovar Typhimurium LT2, the sulfur may be exchanged by selenium, depending on the concentration of selenium in the growth medium. The intermediate in the selenation process is a geranylated derivative (c)mnm⁵ges²U34 (ge, denotes a geranyl group covalently bound to the s²-group) and it is present in the wild type bacteria at a level of only a few percent [26].