DnaJ, DnaK and GrpE make together a molecular chaperone system of the heat shock protein 70. The DnaJ protein originally identified in Escherichia coli gave the beginning of the DnaJ protein family, which now consists of over 20 members now of both prokaryotic and eukaryotic origin. The proteins of the DnaJ family are phylogenetically highly conserved and they show very similar modular architecture. They are involved at all stages of the cellular metabolism, during protein biosynthesis and maturation, in rearrangements of cellular macromolecules during functional cycles of assembly and disassembly, and of course in the protection against environmental stress. Some of the latest research has shown that a DnaJ homolog is related to tumor suppression - the Tid56 putative protein, a product of the lethal(2)tumorous imaginal discs gene.