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Free keywords:
Animals
Bacterial Proteins/chemistry/metabolism
Binding, Competitive
Chloramphenicol O-Acetyltransferase/biosynthesis
Dogs
Escherichia coli/*metabolism
Escherichia coli Proteins
HSP40 Heat-Shock Proteins
Heat-Shock Proteins/biosynthesis/*chemistry/*metabolism
Kinetics
Luciferases/biosynthesis
Microsomes/metabolism
Mitochondria/metabolism
Pancreas/metabolism
Protein Binding
Protein Biosynthesis
Protein Folding
Protein Processing, Post-Translational
Rabbits
Reticulocytes
Saccharomyces cerevisiae/metabolism
Abstract:
Recent evidence supports the view that cellular protein folding may be mediated by molecular chaperones. A fundamental question concerns the stage in its biogenesis at which the folding protein makes first contact with these components. We show here by crosslinking that the chaperone DnaJ binds nascent ribosome-bound polypeptide chains as short as 55 residues. Cotranslational binding of DnaJ to firefly luciferase and chloramphenicol acetyltransferase resulted in an arrest of folding as long as the functional partners of DnaJ in Escherichia coli, DnaK and GrpE, were missing. Protein uptake into microsomes and mitochondria was also interrupted by DnaJ. Both folding and post-translational translocation recommenced upon addition of DnaK and GrpE. We propose that DnaJ protects nascent polypeptide chains against aggregation and, in cooperation with Hsp70, controls their productive folding once a complete polypeptide or a polypeptide domain has been synthesized.
