The application may refer to a biological sequence belonging to the state of the art by merely providing the sequence's accession number and its version or release number in a publicly available database, without presenting the sequence itself either in a sequence listing complying with WIPO Standard ST.25 or in any other format.

Since in this case the sequence is already publicly available, the applicant does not need to supply a sequence listing. This applies even if reference is made to these sequences in one or more claims or if the sequences are essential features of the invention or necessary for the prior-art search (see J 8/11). If the European patent application discloses nucleotide or amino acid sequences that are fragments or variants of a prior-art sequence, a sequence listing complying with WIPO Standard ST.25 has to be filed for these sequence fragments or variants (see the Notice from the EPO dated 18 October 2013, OJ EPO 2013, 542, I.1.5). If the database and/or the sequences in question is/are not completely and unambiguously identified, the sequences are not sufficiently disclosed according to Art. 83 and cannot be added to the application to complete the disclosure without contravening Art. 123(2) (see F‑III, 2).

If such insufficiently disclosed sequences are not essential features of the claimed invention, normally no objection is raised. On the other hand, where these sequences are essential features of at least a part of the claimed subject-matter, this results in problems relating to the sufficiency of the original disclosure according to Art. 83, because the nature of the sequences cannot be unambiguously derived from the incomplete or ambiguous reference to the database.

Examples where a biological sequence is considered an essential feature of the invention would be a diagnostic method using a particular nucleic acid sequence or a product made by a biochemical process using an enzyme with a particular amino acid sequence. An example of ambiguous identification would be the citation of an accession number of a certain protein in the database of the European Molecular Biology Laboratory EMBL with no indication of which version number or database release number is meant when there are several such numbers referring to different sequences of the protein.