TIGRFAMs is a collection of manually curated protein families focusing primarily on prokaryotic sequences.It consists of hidden Markov models (HMMs), multiple sequence alignments, Gene Ontology (GO) terminology, Enzyme Commission (EC) numbers, gene symbols, protein family names, descriptive text, cross-references to related models in TIGRFAMs and other databases, and pointers to literature. Originally developed at The Institute for Genomic Research (TIGR) and later at its successor, the J. Craig Venter Institute (JCVI), it is now maintained by the NCBI.