How redundant are the UniProt databases?
Last modified May 30, 2012
Each of the 3 UniProt databases - UniProtKB (Swiss-Prot and TrEMBL), UniParc and UniRef - are 'non-redundant'. However, the definition of 'redundancy' varies among the 3.
Non-redundancy means in:
- UniProtKB/TrEMBL: one record for 100% identical full-length sequences in one species;
- UniProtKB/Swiss-Prot: one record per gene in one species;
- UniParc: one record for 100% identical sequences over the entire length, regardless of the species;
- UniRef100: one record for 100% identical sequences, including fragments, regardless of the species.
- UniProtKB/TrEMBL is 'non-redundant' in the sense that all identical, full-length protein sequences, provided they come from the same species, are represented in a single record. UniProtKB/TrEMBL sequences are translations of CDS submitted to the EMBL-Bank/GenBank/DDBJ databases and cross-references to the original submissions are kept in the entries. Fragments, isoforms, variants and so on, encoded by the same gene, are stored in separate entries.
- UniProtKB/Swiss-Prot is 'non-redundant' in the sense that all protein products encoded by one gene in a given species are represented in a single record. This includes alternative splicing isoforms, fragments, polymorphisms, sequence conflicts, etc. Differences between sequence reports are analyzed, fully documented and reported in the entry. As is the case for UniProtKB/TrEMBL, cross-references to the original submissions to EMBL-Bank/GenBank/DDBJ databases are kept (see for instance, Q9BXB7).
- How are protein sequence variety and protein diversity represented in UniProtKB?
- What is the canonical sequence? Are all isoforms described in one entry?
- When different genes in the same species give rise to the same protein sequence, they are merged in a single UniProtKB/Swiss-Prot record and the gene names are listed in the gene name subsection. See for example the entry for human histone H3.1 (P68431).
- 'Non-redundancy' in UniProtKB/Swiss-Prot implies that identical sequences are represented in a single record. However, if identical protein sequences are produced in different species, they are stored in different records (e.g. ubiquitin).
- Manual annotation in UniProtKB/Swiss-Prot consists of merging all UniProtKB/TrEMBL entries corresponding to protein products encoded by the same gene and documenting all differences. Once the manually annotated UniProtKB/TrEMBL entries are integrated into UniProtKB/Swiss-Prot, they are automatically removed from UniProtKB/TrEMBL. In this sense, Swiss-Prot and TrEMBL are not redundant with one another. However, merging of new UniProtKB/TrEMBL to existing UniProtKB/Swiss-Prot entries is performed manually - at least partially - in order to ensure that all information contained in the UniProtKB/TrEMBL entry is correctly integrated into UniProtKB/Swiss-Prot. For example, additional publications present in the new UniProtKB/TrEMBL entry have to be critically reviewed and the UniProtKB/Swiss-Prot entry updated accordingly. Given this manual curation effort and the increasing amount of protein sequence data from high-throughput cDNA or genome sequencing projects, it is not possible to ensure non-redundancy at this level. Therefore there can be 100% identical sequences for the same species in UniProtKB/Swiss-Prot and UniProtKB/TrEMBL.
UniParc is 'non-redundant' in the sense that all identical protein sequences are stored in a single record regardless of the species. Each record is characterized by a unique identifier, UPI. For example, identical ubiquitin sequences from various organisms can be found in UniParc record UPI00000006C4.
Three UniRef databases - UniRef100, UniRef90 and UniRef50 - merge sequences automatically across species.
UniRef100 is 'non-redundant' in the sense that identical sequences and subfragments are presented as a single entry. For example, see the UniRef100 cluster for ubiquitin, which contains 100% identical sequences from many different organisms.