THE TAIL OF A CHAPERONIN - THE C-TERMINAL REGION OF ESCHERICHIA-COLI GROEL PROTEIN

The active form of the HSP60 molecular chaperone of Escherichia coil, GroEL, is a pair of seven-membered rings. We have used site-directed m utagenesis to construct forms of the 547-amino-acid monomer truncated at the C-terminus. We show here that forms that are 520 amino acids lo ng or longer are close to being fully functional. Removing one further amino acid, however, results in a protein, GroEL519, which retains li ttle function. This truncated form is metabolically stable but is not recovered from the cell in particle form. When synthesized at high lev els, it prevents the normal assembly of GroEL547 present in the same c ell. When synthesized at low levels, it can be included, probably at l ow molar ratios, in particles formed by assembly-competent forms of Gr oEL. This can be seen as partial complementation of the temperature-se nsitive mutant groEL44. We conclude that amino acid 520 is crucial for particle assembly. GroEL516 has in vivo properties similar to those o f GroEL519, but the still shorter form, GroEL504, appears to be inacti ve.