O ▁cluster , ▁m rb J , ▁enc odes ▁a ▁two - module ▁non rib os om al ▁pe pt ide ▁synth et ase . ▁Mir ub act in ▁assembly ▁uses ▁two ▁non prote in ogen ic ▁units , ▁ 2 , 3 - d ih ydro xy ben zo ic ▁acid ▁( 2 , 3 - D H B ) ▁and ▁ δ - N - form yl - δ - N - h ydro xy orn ith ine ▁( f h Or n ). ▁Mr b C ▁and ▁Mr b D ▁work ▁to ▁activ ate ▁and ▁incorpor ate ▁ 2 , 3 - D H B ▁into ▁the ▁non rib os om al ▁pe pt ide ▁synth esis . ▁The ▁ 2 , 3 - D H B ▁is ▁incorpor ated ▁on ▁both ▁the ▁N - ▁and ▁C - ▁term ini , ▁and ▁is ▁attached ▁to ▁the ▁ δ - N - h ydro x yl ▁group ▁of ▁f h Or n ▁to ▁form ▁a ▁O - ac yl - h ydro x am ic ▁acid ▁est er . ▁At ▁the ▁start ▁of ▁the ▁assembly , ▁ 2 , 3 - D H B ▁is ▁activ ated ▁by ▁Mr b C ▁and ▁subsequently ▁passed ▁to ▁Mr b D , ▁where ▁it ▁is ▁attached ▁to ▁the ▁arg in ine ▁in ▁the ▁first ▁module ▁by ▁Mr b J . ▁The ▁second ▁module ▁of ▁Mr b J ▁incorpor ates ▁f h Or n , ▁which ▁is ▁generated ▁by ▁the ▁tail oring ▁en zym es