BRITE functional hierarchies

Orthologs, modules and networks
  00001  KEGG Orthology (KO)

Protein families: metabolism
  01000  Enzymes
  01001  Protein kinases
  01009  Protein phosphatases and associated proteins
  01002  Peptidases and inhibitors
  01003  Glycosyltransferases
  01004  Lipid biosynthesis proteins
  01006  Prenyltransferases
  01007  Amino acid related enzymes
  00199  Cytochrome P450

Protein families: genetic information processing
  03000  Transcription factors
  03021  Transcription machinery
  03019  Messenger RNA biogenesis
  03041  Spliceosome
  03011  Ribosome
  03009  Ribosome biogenesis
  03016  Transfer RNA biogenesis
  03012  Translation factors
  03110  Chaperones and folding catalysts
  04131  Membrane trafficking
  04121  Ubiquitin system
  03051  Proteasome
  03032  DNA replication proteins
  03036  Chromosome and associated proteins
  03400  DNA repair and recombination proteins
  03029  Mitochondrial biogenesis

Protein families: signaling and cellular processes
  02000  Transporters
  02044  Secretion system
  02042  Bacterial toxins
  04812  Cytoskeleton proteins
  04147  Exosome
  02048  Prokaryotic defense system
  04030  G protein-coupled receptors
  04050  Cytokine receptors
  04054  Pattern recognition receptors
  03310  Nuclear receptors
  04040  Ion channels
  04031  GTP-binding proteins
  04052  Cytokines and growth factors
  04515  Cell adhesion molecules
  04090  CD molecules
  00535  Proteoglycans
  00536  Glycosaminoglycan binding proteins
  00537  Glycosylphosphatidylinositol (GPI)-anchored proteins
  04091  Lectins
  04990  Domain-containing proteins not elsewhere classified

Viral protein families
RNA family