| Code | Meaning | Description |
| ID | Identification | Contains identifying information and characteristics of the sequence |
| AC | Accession number(s) | Release-to-release stable identifiers |
| DT | Date | When the entry was created, or when the sequence or annotation was modified |
| DE | Description | The name of the protein, often a function indicator |
| GN | Gene name(s) | The gene(s) that code for the protein |
| OS | Organism species | The organism from which the sequence is derived |
| OG | Organelle | If the sequence is non-chromosomal in origin |
| OC | Organism classification | The taxonomic class to which the organism belongs |
| OX | Taxonomy x-reference(s) | The NCBI TaxID for the OC line |
| RN | Reference number | The sequential number of the literature citation within the entry |
| RP | Reference position | The type of data, and the position in the sequence to which the citation refers |
| RC | Reference comment(s) | Comments relevant to the reference cited |
| RX | Reference x-reference(s) | Bibliographic cross-reference, such as PubMed ID |
| RA | Reference authors | Authors of the citation |
| RT | Reference title | Title of the citation |
| RL | Reference location | Source of the citation, such as journal, book, or unpublished data |
| CC | Comments | Free text notes about the protein |
| DR | Database x-references | Pointers to sources or related information for the entry |
| KW | Keywords | Indexable indicator of function, structure, or other information |
| FT | Feature table | Annotation of specific residues of the sequence |
| SQ | Sequence header | Marks the beginning of the sequence and provides summary data |
| (no code) | Sequence data | The sequence itself |
| // | Termination line | End of entry |