tokens: The major transcription factors controlling arginine metabolism in Escherichia coli and Bacillus subtilis , ArgR and AhrC , respectively , are homologous multimeric proteins that form l - arginine - dependent DNA - binding complexes capable of repressing transcription of the biosynthetic genes ( both ) , activating transcription of catabolic genes ( AhrC only ) or facilitating plasmid dimer resolution ( both ) .