TRANSLATIONAL AUTOCONTROL OF THE ESCHERICHIA-COLI RIBOSOMAL PROTEIN-S15

When rpsO, the gene encoding the ribosomal protein S15 in Escherichia coli, is carried by a multicopy plasmid, the mRNA synthesis rate of S15 increases with the gene dosage but the rate of synthesis of S15 does not rise. A translational fusion between S15 and β-galactosidase was introduced on the chromosome in a Δlac strain and the expression of β-galactosidase studied under different conditions. The presence of S15 in trans represses the β-galactosidase level five- to sixfold, while the synthesis rate of the S15-β-galactosidase mRNA decreases by only 30 to 50%. These data indicate that S15 is subject to autogenous translational control. Derepressed mutants were isolated and sequenced. All the point mutations map in the second codon of S15, suggesting a location for the operator site that is very near to the translation initiation codon. However, the creation of deletion mutations shows that the operator extends into the 5′ non-coding part of the message, thus overlapping the ribosome loading site. © 1990.