The UniProt format is widely used to represent annotated protein sequences.
It contains several keys and subkeys to describe sequence characteristic.
Each sequence starts by the key ID and terminates by //. The record
can contain more than one sequence. 

Example: 

ID   LV403_HUMAN             Reviewed;         107 AA.
AC   P01717;
DT   21-JUL-1986, integrated into UniProtKB/Swiss-Prot.
DT   21-JUL-1986, sequence version 1.
DT   12-DEC-2006, entry version 49.
DE   Ig lambda chain V-IV region Hil.
OS   Homo sapiens (Human).
OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; 
OC   Mammalia; Eutheria; Euarchontoglires; Primates; Haplorrhini; 
OC   Catarrhini; Hominidae; Homo. 
OX   NCBI_TaxID=9606;
RN   [1]
RP   PROTEIN SEQUENCE.
RX   MEDLINE=78187276; PubMed=418804 [NCBI, ExPASy, EBI, Israel, Japan]; DOI=10.1021/bi00602a021;
RA   Lopez de Castro J.A., Chiu Y.-Y.H., Poljak R.J.;
RT   "Amino acid sequence of the variable region of the light (lambda)
RT   chain from human myeloma cryoimmunoglobulin IgG Hil.";
RL   Biochemistry 17:1718-1723(1978).
CC   -!- MISCELLANEOUS: The sequence of the C region is apparently
CC       identical with that of human SH lambda chain except in having 155-
CC       Ile (Hil numbering) instead of Val.
CC   -!- MISCELLANEOUS: This chain was isolated from a myeloma protein.
CC   -!- SIMILARITY: Contains 1 Ig-like (immunoglobulin-like) domain.
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DR   PIR; A01983; L4HUHL.
DR   HSSP; P01703; 7FAB. [HSSP ENTRY / SWISS-3DIMAGE / PDB]
DR   SMR; P01717; 3-107.
DR   GO; GO:0005576; C:extracellular region; NAS:UniProtKB.
DR   GO; GO:0003823; F:antigen binding; NAS:UniProtKB.
DR   GO; GO:0006955; P:immune response; NAS:UniProtKB.
DR   InterPro; IPR007110; Ig-like.
DR   InterPro; IPR013783; Ig-like_fold.
DR   InterPro; IPR013106; Ig_V-set.
DR   InterPro; IPR003596; Ig_V-set_sub.
DR   InterPro; Graphical view of domain structure.
DR   Pfam; PF07686; V-set; 1.
DR   Pfam; Graphical view of domain structure.
DR   SMART; SM00406; IGv; 1.
DR   PROSITE; PS50835; IG_LIKE; 1.
DR   BLOCKS; P01717.
DR   ProtoNet; P01717.
DR   DIP; P01717.
DR   ModBase; P01717.
DR   SWISS-2DPAGE; GET REGION ON 2D PAGE.
KW   Direct protein sequencing; Immunoglobulin domain;
KW   Immunoglobulin V region.
FT   CHAIN         1   >107       Ig lambda chain V-IV region Hil.
FT                                /FTId=PRO_0000059846.
FT   DOMAIN        1     97       Ig-like.
FT   NON_TER     107    107
SQ   SEQUENCE   107 AA;  11517 MW;  A5C8AFFE0C0C590A CRC64;
     SYELTQPPSV SVSPGQTARI TCSANALPNQ YAYWYQQKPG RAPVMVIYKD TQRPSGIPQR
     FSSSTSGTTV TLTISGVQAE DEADYYCQAW DNSASIFGGG TKLTVLG
//