Programmed Ribosomal Frameshifting Generates a Copper Transporter and a Copper Chaperone from the Same Gene

Abstract

Summary Metal efflux pumps maintain ion homeostasis in the cell. The functions of the transporters are often supported by chaperone proteins, which scavenge the metal ions from the cytoplasm. Although the copper ion transporter CopA has been known in Escherichia coli, no gene for its chaperone had been identified. We show that the CopA chaperone is expressed in E. coli from the same gene that encodes the transporter. Some ribosomes translating copA undergo programmed frameshifting, terminate translation in the -1 frame, and generate the 70 amino acid-long polypeptide CopA(Z), which helps cells survive toxic copper concentrations. The high efficiency of frameshifting is achieved by the combined stimulatory action of a ‘slippery’ sequence, an mRNA pseudoknot, and the CopA nascent chain. Similar mRNA elements are not only found in the copA genes of other bacteria but are also present in ATP7B, the human homolog of copA, and direct ribosomal frameshifting in vivo.

Novel pipeline identifies new upstream ORFs and non-AUG initiating main ORFs with conserved amino acid sequences in the 5′ leader of mRNAs in Arabidopsis thaliana

“…The other four CPuORFs could also induce stalling as exemplified by the CPuORF present on the LHY mRNA. Possibly, these uCCRs are prone to ribosomal frameshifting, a process where the ribosome shifts its frame during the elongation phase of translation of an ORF (Kurian et al 2011;Yordanova et al 2015;Gao and Simon 2016;Meydan et al 2017). To our knowledge, ribosomal frameshifting in plants has only been shown on viral RNA (Gao and Simon 2016).…”

A [Cu]rious Ribosomal Profiling Pattern Leads to the Discovery of Ribosomal Frameshifting in the Synthesis of a Copper Chaperone

“…Irrespective of functional aspects, encoding both CopZ and CopA from a gene named copA before this dual coding discovery creates a minor nomenclature dilemma. Meydan et al (2017) provide evidence that the À1 ribosomal frameshift stimulatory elements are present in a wide range of bacterial species, strongly implying positive selective pressure for co-expression of the copper efflux pump protein and its small intracellular chaperone. In addition, they also report that the human ATP7B gene encoding a copper-transporting ATPase 2 contains the same C_CCA_AAG pattern as in E. coli copA.…”

“…For long new frame ORFs, the framing information available in some profiling datasets is pertinent. In contrast, irrespective of whether framing information is available, a sudden drop in ribosome density within an ORF (Figure 1), as described in Meydan et al (2017), may indicate frameshift-mediated alternative frame termination. Exploitation, in diverse ways, of the dynamic nature of decoding is by now well established, and prior views of decoding rigidly following set rules has been laid to rest, but the extent of its utilization remains largely unknown.…”

“…In E. coli no separate copper chaperone has been identified, though a copper binding domain was identified at the N terminus of its copper efflux pump protein, CopA (Drees et al, 2015). In this issue, Meydan et al (2017) reanalyze E. coli ribosome profiling data focusing on an unusual and sudden decrease in the number of ribosome protected fragments aligning 3 0 of codon 70 in the copA coding sequence. They show that a substantial proportion of ribosomes translating the copA mRNA slip backward by a single nucleotide into an alternative reading frame where they almost immediately encounter a stop codon.…”

Bacterial copper storage proteins

“…CopA can work either alone or in concert with the ATOX1/Atx1 homologue CopZ to remove cytosolic Cu (5-7, 20-23, 27, 28). It has recently been found that in bacteria not previously thought to possess this Cu metallochaperone such as E. coli, CopZ can be made from the CopA gene by 'programmed ribosomal frameshifting' (29).…”