ELUCIDATION OF THE SUBUNIT ORIENTATION IN CCT (CHAPERONIN CONTAINING TCP1) FROM THE SUBUNIT COMPOSITION OF CCT MICRO-COMPLEXES

A collection of chaperonin containing TCP1 (CCT) micro-complexes that are comprised of subsets of the constitutively expressed CCT subunits have been identified, These CCT micro-complexes have mel. wts ranging from 120 to 250 kDa and are present in cells at lower abundance (<5%) as compared with intact CCT. Biochemical characterization of these mic ro-complexes has shown that several are comprised of two different typ es of CCT submit, Furthermore, it was observed that each subunit assoc iates with only one or two other different types of subunit, suggestin g that each subunit has fixed partners, This observation, together wit h CCT gene counting being concordant with the 8-fold structural symmet ry, is consistent with predictions derived from analysis of the primar y structures of these submits concerning inter-subunit interactions, a nd implies a unique topology of the subunits constituting the torodial ring in CCT. The series of subunit-subunit association patterns deter mined from CCT micro-complexes has provided information to infer, from the 5040 (7!factorial) combinatorial possibilities, one probable subu nit orientation within the toroidal ring.