Prokaryotic and eukaryotic organisms respond to heat shock or other environmental stress by the induction of the synthesis of proteins collectively known as heat-shock proteins (hsp) [1]. Amongst them is a family of proteins, with an average molecular weight of 90 Kd, known as the hsp90 proteins. Proteins known to belong to this family are:

• Escherichia coli and other bacteria heat shock protein c62.5 (gene htpG).
• Vertebrate hsp 90-α (hsp 86) and hsp 90-β (hsp 84).
• Drosophila hsp 82 (hsp 83).
• Trypanosoma cruzi hsp 85.
• Plants Hsp82 or Hsp83.
• Yeast and other fungi HSC82, and HSP82.
• The endoplasmic reticulum protein 'endoplasmin' (also known as Erp99 in mouse, GRP94 in hamster, and hsp 108 in chicken).

The exact function of hsp90 proteins is not yet known. In higher eukaryotes, hsp90 has been found associated with steroid hormone receptors, with tyrosine kinase oncogene products of several retroviruses, with eIF2α kinase, and with actin and tubulin. Hsp90 are probable chaperonins that possess ATPase activity [2,3].

As a signature pattern for the hsp90 family of proteins, we have selected a highly conserved region found in the N-terminal part of these proteins.