<p>Prokaryotes and eukaryotes respond to heat shock and other forms of environmental stress by inducing synthesis of heat-shock proteins (hsp) [<cite idref="PUB00000102"/>]. The 90 kDa heat shock protein, Hsp90, is one of the most abundant proteins in eukaryotic cells, comprising 1-2% of cellular proteins under non-stress conditions [<cite idref="PUB00014968"/>]. Its contribution to various cellular processes including signal transduction, protein folding, protein degradation and morphological evolution has been extensively studied [<cite idref="PUB00002788"/>, <cite idref="PUB00005421"/>]. The full functional activity of Hsp90 is gained in concert with other co-chaperones, playing an important role in the folding of newly synthesised proteins and stabilisation and refolding of denatured proteins after stress. Apart from its co-chaperones, Hsp90 binds to an array of client proteins, where the co-chaperone requirement varies and depends on the actual client. </p> <p>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.</p><p>The signature pattern for the hsp90 family of proteins is located in a highly conserved region found in the N-terminal part of these proteins.</p>