AUU-to-AUG mutation in the initiator codon of the translation initiation factor IF3 abolishes translational autocontrol of its own gene (infC) in vivo. Proc Natl Acad Sci USA 84: 4022

Institute of Physical and Chemical Biology, Lutetia Parisorum, Île-de-France, France
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/1987; 84(12):4022-5. DOI: 10.1073/pnas.84.12.4022
Source: PubMed


We previously showed that Escherichia coli translation initiation factor IF3 regulates the expression of its own gene infC at the translational level in vivo. Here we create two alterations in the infC gene and test their effects on translational autocontrol of infC expression in vivo by measuring beta-galactosidase activity expressed from infC-lacZ gene fusions under conditions of up to 4-fold derepression or 3-fold repression of infC expression. Replacement of the infC promoter with the trp promoter deletes 120 nucleotides of the infC mRNA 5' to the translation initiation site without affecting autogenous translational control. Mutation of the unusual AUU initiator codon of infC to the more common AUG initiator codon abolishes translation initiation factor IF3-dependent repression and derepression of infC expression in vivo. These results establish the AUU initiator codon of infC as an essential cis-acting element in autogenous translational control of translation initiation factor IF3 expression in vivo.

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    • "This is analogous to the autoregulatory control of synthesis of bacterial initiation factor 3 (IF3), a protein which like eIF1 discriminates between initiation at AUG and near-cognate non-AUG codons. Initiation of IF3 mRNA translation is at an AUU codon and high IF3 levels result in reduced initiation at this codon, reducing IF3 synthesis (17,18). Autoregulation at the level of translation also controls the expression of other translation factors (19). "
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    ABSTRACT: An AUG in an optimal nucleotide context is the preferred translation initiation site in eukaryotic cells. Interactions among translation initiation factors, including eIF1 and eIF5, govern start codon selection. Experiments described here showed that high intracellular eIF5 levels reduced the stringency of start codon selection in human cells. In contrast, high intracellular eIF1 levels increased stringency. High levels of eIF5 induced translation of inhibitory upstream open reading frames (uORFs) in eIF5 mRNA that initiate with AUG codons in conserved poor contexts. This resulted in reduced translation from the downstream eIF5 start codon, indicating that eIF5 autoregulates its own synthesis. As with eIF1, which is also autoregulated through translation initiation, features contributing to eIF5 autoregulation show deep evolutionary conservation. The results obtained provide the basis for a model in which auto- and cross-regulation of eIF5 and eIF1 translation establish a regulatory feedback loop that would stabilize the stringency of start codon selection.
    Full-text · Article · Dec 2011 · Nucleic Acids Research
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    • "The start codon of the infC gene contained on these plasmids has been changed to AUG in order to eliminate the potential autoregulation by IF3 of its own gene infC (Butler et al., 1987). Single-base mutations in the -35 and -10 elements of the P2 promoter were introduced by site-directed mutagenesis using primers HP1530–HP1531 or HP1532–HP1533 respectively. "
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    ABSTRACT: RNase Y is a novel endoribonuclease affecting global mRNA metabolism. We show that this nuclease affects the expression of the Bacillus subtilis infC-rpmI-rplT operon, encoding translation initiation factor IF3 and the ribosomal proteins L35 and L20. This operon is autoregulated by a complex L20-dependent transcription attenuation mechanism. L20 binds to a phylogenetically conserved domain on the 5' untranslated region of the infC mRNA which mimics the L20 binding sites on 23S rRNA. We have identified a second promoter (P1) upstream of the previously identified promoter (P2). The P1, but not the P2, readthrough transcript is stabilized in a strain depleted for RNase Y. However, under these conditions infC biosynthesis is repressed threefold. We show that the unprocessed P1 transcript is non-functional for IF3 translation but fully competent to express the co-transcribed ribosomal protein genes. RNase Y cleavage of the P1 transcript creates an entry site for the 5'-3' exonucleolytic activity of RNase J1 which degrades the infC mRNA when translation initiation efficiency is low. A second RNase Y cleavage is crucial for initiating degradation of the prematurely terminated infC leader RNAs, including the L20 operator complex, which permits efficient recycling of the L20 protein.
    Full-text · Article · Aug 2011 · Molecular Microbiology
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    • "The discovery that this gene could not be overexpressed in E. coli suggested that it is regulated at the level of translation by a negative feedback loop (Fig. 2; Gold et al. 1984; Butler et al. 1986) and that the AUU initiation codon plays a central role in this regulation. In fact, replacing the AUU codon with an AUG abolishes this autogenous regulation and boosts IF3 production 10-fold (Butler et al. 1987). Furthermore, replacing the AUG initiation codon of a neighboring gene thrS with AUU also placed this gene under IF3 autoregulatory control (Sacerdot et al. 1996). "
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    ABSTRACT: In both prokaryotes and eukaryotes, the expression of a large number of genes is controlled by negative feedback, in some cases operating at the level of translation of the mRNA transcript. Of particular interest are those cases where the proteins concerned have cell-wide function in recognizing a particular codon or RNA sequence. Examples include the bacterial translation termination release factor RF2, initiation factor IF3, and eukaryote poly(A) binding protein. The regulatory loops that control their synthesis establish a negative feedback control mechanism based upon that protein's RNA sequence recognition function in translation (for example, stop codon recognition) without compromising the accurate recognition of that codon, or sequence during general, cell-wide translation. Here, the bacterial release factor RF2 and initiation factor IF3 negative feedback loops are reviewed and compared with similar negative feedback loops that regulate the levels of the eukaryote release factor, eRF1, established artificially by mutation. The control properties of such negative feedback loops are discussed as well as their evolution. The role of negative feedback to control translation factor expression is considered in the context of a growing body of evidence that both IF3 and RF2 can play a role in stimulating stalled ribosomes to abandon translation in response to amino acid starvation. Here, we make the case that negative feedback control serves primarily to limit the overexpression of these translation factors, preventing the loss of fitness resulting from an unregulated increase in the frequency of ribosome drop-off.
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