The TCP-1 protein [1,2] (Tailless Complex Polypeptide 1) was first identified in mice where it is especially abundant in testis but present in all cell types. It has since been found and characterized in many other mammalian species, in Drosophila and in yeast. TCP-1 is a highly conserved protein of about 60 Kd (556 to 560 residues) which participates in a hetero-oligomeric 900 Kd double-torus shaped particle [3] with 6 to 8 other different subunits. These subunits, the chaperonin containing TCP-1 (CCT) subunit β, γ, delta, epsilon, zeta and eta are evolutionary related to TCP-1 itself [4,5]. The CCT is known to act as a molecular chaperone for tubulin, actin and probably some other proteins.

The CCT subunits are highly related to archebacterial counterparts:

• TF55 and TF56 [6], a molecular chaperone from Sulfolobus shibatae. TF55 has ATPase activity, is known to bind unfolded polypeptides and forms a oligomeric complex of two stacked nine-membered rings.
• Thermosome [7], from Thermoplasma acidophilum. The thermosome is composed of two subunits (α and β) and also seems to be a chaperone with ATPase activity. It forms an oligomeric complex of eight-membered rings.

The TCP-1 family of proteins are weakly, but significantly [8], related to the cpn60/groEL chaperonin family (see <PDOC00268>).

As signature patterns of this family of chaperonins, we chose three conserved regions located in the N-terminal domain.

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