INSD (the International Nucleotide Sequence Databases) are composed of DDBJ, EMBL and GenBank, and collect experimentally determined nucleotide sequence data and the TPA data. INSD accept the direct submission of the sequence data that is made online by researchers all over the world. Each of INSD serves a data submission tool on its website. The data is submitted in the unit of "entry".
A unique accession number issued by INSD for each entry is defined as the INSD accession number. The number is internationally recognized to guarantee the submitter the property of the submitted and published data.
The accession number is composed of 1 alphabet letter and 5 digits (ex. A12345) or 2 alphabet letters and 6 digits (ex. AB123456). The alphabet part is called "prefix". Please refer the prefix list.
Though often confused, the followings are not the INSD accession number;
Please refer here for more information about the prefix for protein_id.