Enhancement of translation by the epsilon element is independent of the sequence of the 460 region of 16S rRNA

Abstract

The epsilon enhancer element is a pyrimidine-rich sequence that increases expression of T7 gene 10 and a number of Escherichia coli mRNAs during initiation of translation and inhibits expression of the recF mRNA during elongation. Based on its complementarity to the 460 region of 16S rRNA, it has been proposed that epsilon exerts its enhancer activity by base pairing to this complementary rRNA sequence. We have tested this model of enhancer action by constructing mutations in the 460 region of 16S rRNA and examining expression of epsilon-containing CAT reporter genes and recF-lacZ fusions in strains expressing the mutant rRNAs. Replacement of the 460 E.coli stem-loop with that of Salmonella enterica serovar Typhimurium or a stem-loop containing a reversal of all 8 bp in the helical region produced fully functional rRNAs with no apparent effect on cell growth or expression of any epsilon-containing mRNA. Our experiments confirm the reported effects of the epsilon elements on gene expression but show that these effects are independent of the sequence of the 460 region of 16S rRNA, indicating that epsilon-rRNA base pairing does not occur.

Figure 1

The secondary (left) and tertiary (right) (19) structures of bacterial 16S rRNA with the regions of interest indicated.

Figure 2

Secondary structures of the 460 stem–loop from E.coli (left), S.enterica serovar Typhimurium (middle) and a mutant containing a reversal of all 8 bp of the E.coli stem (right). Nucleotides differing from the E.coli wild-type sequence are indicated in bold.