The chaperonin from the acidothermopilic archaeon, Sulfolobus sp, Strain 7, is composed of two kinds of subunits designated as Scp alpha and Scp beta. In this study, we characterized the recombinant Scp alpha and Scp beta, which were separately expressed in Escherichia coli, Both of them were able to assemble to homo-oligomeric double-ring complexes, similar to subunits of group II chaperonins from Thermoplasma acidophilum and Thermococcus strain KS-1, Both complexes have no or at most trace ATPase activities, However, they could arrest spontaneous refolding of chemically denatured enzyme in the same way as the purified Sulfolobus chaperonin, We found that they dissociated in the presence of 15% ethanol to monomers, which spontaneously assembled to oligomers when concentrated in the absence of ethanol, Both the reconstituted homo-oligomers were unstable, and easily dissociated to monomers, Further structural and functional characterization is necessary to elucidate if these homooligomers exist and if so, their function in vivo. (C) 1998 Academic Press.