Structure Integration with Function, Taxonomy and Sequence (SIFTS) is a project in the PDBe KB resource for residue level mapping between UniProt and PDB entries. SIFTS also provides annotation from the IntEnz, GO, InterPro, Pfam, CATH, SCOP, PubMed, Ensembl and Homologene resources. The information is updated and released every week concurrently with the release of new PDB entries and is widely used by resources such as RCSB PDB, PDBj, PDBsum, Pfam, SCOP and InterPro.