the small subunit , which contains 10 conserved cysteine residues , is likely to coordinate at least 2 iron-sulfur clusters , while the finding of a selenocysteine codon ( tga ) near the 3 ' end of the [ nifese ] large-subunit gene matched by a regular cysteine codon ( tgc ) in the [ nife ] large-subunit gene indicates the presence of some of the ligands to the active-site nickel in the large subunit .
C0074289
selenocysteine
C0010654
cysteine