2 CLASSES OF EXTRAGENIC SUPPRESSOR MUTATIONS IDENTIFY FUNCTIONALLY DISTINCT REGIONS OF THE GROEL CHAPERONE OF ESCHERICHIA-COLI

The GroES and GroEL proteins of Escherichia coli function together as the GroE molecular chaperone machine to (i) prevent denaturation and a ggregation and (ii) assist the folding and oligomerization of other pr oteins without being part of the final structure. Previous genetic and biochemical analyses have determined that this activity requires inte ractions of the GroES 7-mer with the GroEL 14-mer. Recently, we have i dentified a region of the GroES protein that interacts with the GroEL protein. To identify those residues of the GroEL protein that interact with GroES, we have exploited the thermosensitive phenotype of strain s bearing mutations at one or the other of two GroEL-interacting resid ues of GroES. We have isolated, cloned, acid sequenced six suppressor mutations in groEL, three independent isolates for each groES mutant. Changes of only three different amino acid substitutions in GroEL prot ein were found among these six groEL suppressor mutations. On the basi s of a number of in vivo analyses of the chaperone activity of various combinations of groES mutant alleles and groEL suppressor alleles, we propose that an amino-proximal region of the GroEL protein which incl udes amino acid residues 174 and 190 interacts with GroES and that a c arboxyl-proximal region which includes residue 375 interacts with subs trate proteins.