Non-Standard Residue

Any residue not included in the list of Standard Residues is considered Non-Standard.

Examples:

• SEP and TPO in 1bkx
• 1MA, 2MG, 5MC, 5MU, 7MG, H2U, M2G, OMC, OMG, PSU, and YG in 1evv
• MSE in 2ab5

Note: the former scheme of designating modified standard nucleotides with plus signs (+A, +C, +G, +I, +T, +U) was discontinued in the PDB remediation project, effective August 1, 2007.