The integrated annotations for Ubiquitin and Ubiquitin-like Conjugation Database (iUUCD) is a comprehensive database containing 136,512 potential proteins collected from 148 sequenced proteomes. To date, iUUCD has included E1s (ubiquitin-activating enzymes), E2s (ubiquitin-conjugating enzymes), E3s (ubiquitin ligases), DUBs (deubiquitinating enzymes), UBDs (ubiquitin-binding domain containing proteins) and ULDs (ubiquitin like domain containing proteins) of ubiquitin and ubiquitin-like modifications.

    iUUCD classifies all the E1s，E2s, E3s, DUBs, UBDs and ULDs into 74 families from 68 animals (Ensembl), 39 plants (EnsemblPlants) and 41 fungi (EnsemblFungi). Besides, iUUCD provides annotation information for all these proteins in the database, including cancer mutation, single nucleotide polymorphism (SNP), mRNA expression, DNA & RNA element, protein-protein interaction, protein structure, disease-associated information, post-translational modifications (PTMs), DNA methylation, protein expression (proteomics), protein information and so on. Users can browse the database:(i) By species; (ii) By classifications.

	Animals	Plants	Fungi

	Enzymes	UBDs	ULDs