DnaK-dependent ribosome biogenesis in Escherichia coli : competition for dominance between the alleles dnaK756 and dnaK ⁺

Abstract

The Escherichia coli chaperone DnaK is vital for many cellular functions, including ribosome biogenesis at high temperature. Thus, the dnaK756-ts (λ ^R) mutant, at the non-permissive temperature, is inhibited at a late stage of ribosome assembly, yielding 21S, 32S and 45S precursor particles. This defect, unlike the λ resistance and thermosensitivity phenotypes, is not complemented by lysogenisation with a transducing phage λ dnaK ⁺ bearing the wild-type dnaK gene. However this dominant phenotype becomes recessive when dnaK ⁺ is expressed from a medium-copy-number plasmid. On the other hand, an excess of DnaK causes an unexpected dominant-lethal effect of the dnaK756 allele near non-permissive temperatures. This interplay between the dnaK ⁺and dnaK756 alleles supports the idea of that DnaK oligomers form in the cell.