Translational coupling of the two proximal genes in the S10 ribosomal protein operon of Escherichia coli

Abstract

We have examined the translational coupling between the first two genes in the S10 ribosomal protein operon. We isolated mutations blocking the translation of the first gene of the operon, coding for S10, and monitored their effects on translation of the downstream gene, coding for L3. All of the mutations inhibiting S10 synthesis also affected the synthesis of L3. However, these experiments were complicated by decreased mRNA synthesis resulting from transcription polarity, which we could only partially eliminate by using a rho-100 strain. To completely eliminate the problem of transcription polarity and obtain a more accurate measurement of the coupling, we replaced the natural S10 promoter with a promoter used by the bacteriophage T7 RNA polymerase. As expected, the T7 RNA polymerase was not subject to transcription polarity. Using this system, we were able to show that a complete abolishment of S10 translation resulted in an 80% inhibition of L3 synthesis. Other experiments show that the synthesis of L3 goes up as a function of increasing S10 synthesis, but the translational coupling does not assure strictly proportional output from the two genes.The majority of the ribosomal protein (r-protein) genes of Escherichia coli are organized in multicistronic transcription units (14). The translation of most of these r-protein operons is under autogenous control. That is, one of the r-proteins encoded by a given transcription unit functions as a repressor of the translation of most or all genes in the unit (14,22).The S10 operon codes for 11 r-proteins. Translation of this r-protein operon is regulated by L4, the product of the third gene of the operon (9, 31). Genetic analysis has shown that the target for translation control of the S10 operon is located in the leader (9; L. P. Freedman, Ph.D. thesis, University of Rochester, Rochester, N.Y., 1985). This suggests that, whereas the first gene of the operon is under direct translational inhibition by L4, the regulation of the downstream genes is due to some indirect mechanism, analogous to what has been shown for several other r-protein operons (17,30,32).It has been proposed that the propagation of translational regulation down an r-protein operon depends on translational coupling (22,32), a phenomenon first demonstrated in the tryptophan operon by Oppenheim and Yanofsky (23). When two genes are translationally coupled, efficient translation of a downstream gene depends on the translation of the adjacent upstream gene. Translationally coupled genes are often separated by intercistronic regions which are 3 bases or less (2-4, 23, 25); in several of these cases, the termination codon of the upstream gene even overlaps with the initiation codon of the downstream gene. It has been speculated that the short distance between the genes is essential for efficient translational coupling (23), although coupling has been reported in several r-protein operons which contain genes separated by longer intercistronic regions (17, 30).We have investigated the extent of coupling betw...

Widespread Selection for Local RNA Secondary Structure in Coding Regions of Bacterial Genes

“…eron (nuoF, nuoH), the S10 operon (rplD, rplB), and the spc operon (rplX, rplR). Interestingly, at least three of these operons-atp, S10 and spc-are known to be regulated at the level of translation rate and/or differential mRNA stability (Freedman et al 1987;Lindahl et al 1989;Mattheakis et al 1989;McCarthy 1990;McCarthy et al 1991). As systematic annotation of operons becomes available for other bacteria, it will be of interest to determine how widespread this association between secondary structure potential and location within operons may be.…”

Regulation of Ribosome Biosynthesis in Escherichia coli

“…In this case, it is probable that L4 binding stabilizes the ribosome-mRNA complex in a pre-initiation state that is not competent to continue along the initiation pathways as described below for the operon. The inhibition of translation initiation would block translation of the first gene in this operon, S10, whereas expression of the other downstream genes would be inhibited by disrupting translational coupling [76].…”

An S6:S18 complex inhibits translation of E. coli rpsF

“…This enables regulation of multiple ribosomal protein genes within an operon because many ribosomal protein genes display translational coupling, in which inhibition of translation for a gene at the 5 ′ end of a transcript also represses translation of the remaining downstream genes (Baughman and Nomura 1983;Thomas et al 1987;Lindahl et al 1989). In addition, inhibition of translation frequently leads to an increased degradation rate for the transcript, further repress-ing gene expression (Deana and Belasco 2005).…”