In organisms like?Archaeoglobus fulgidus?lacking EC?6.1.1.16?(cysteine¡ªtRNA ligase) for the direct Cys-tRNACys?formation, Cys-tRNACys?is produced by an indirect pathway, in which EC?6.1.1.27?ligates?O-phosphoserine to tRNACys, and EC?2.5.1.73?(O-phospho-L-seryl-tRNA: Cys-tRNA synthase) converts the produced?O-phospho-L-seryl-tRNACys?to Cys-tRNACys. The SepRS/SepCysS pathway is the sole route for cysteine biosynthesis in the organism [1].?Methanosarcina mazei?can use both pathways, the direct route using EC?6.1.1.16?(cysteine¡ªtRNA ligase) and the indirect pathway with EC?6.1.1.27?and EC?2.5.1.73?(O-phospho-L-seryl-tRNA: Cys-tRNA synthase) [2].