BRITE functional hierarchies

Orthologs and modules
  00001  KEGG Orthology (KO)

Protein families: metabolism
  01000  Enzymes
  01002  Peptidases and inhibitors

Protein families: genetic information processing
  03000  Transcription factors
  03021  Transcription machinery
  03019  Messenger RNA biogenesis
  03011  Ribosome
  03009  Ribosome biogenesis
  03016  Transfer RNA biogenesis
  03012  Translation factors
  03110  Chaperones and folding catalysts
  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
  04147  Exosome
  02048  Prokaryotic defense system

Viral protein families
RNA family
  03100  Non-coding RNAs