Prokaryotes and eukaryotes respond to heat shock and other forms of environmental stress by inducing synthesis of heat-shock proteins. The 90 kDa heat shock protein, Hsp90, is one of the most abundant proteins in eukaryotic cells. Its contribution to various cellular processes including signal transduction, protein folding, protein degradation and morphological evolution has been extensively studied. The sequences of hsp90s show a distinctive domain structure, with a highly-conserved N-terminal domain separated from a conserved, acidic C-terminal domain by a highly-acidic, flexible linker region. This model is 2cg9 in the molecular protean database (pdb).