tRNA^Pro‐mediated downregulation of elongation factor P is required for mgtCBR expression during Salmonella infection

Abstract

Bacterial ribosome requires elongation factor P to translate fragments harbouring consecutive proline codons. Given the abundance of ORFs with potential EF-P regulated sites, EF-P was assumed to be constitutively expressed. Here, we report that the intracellular pathogen Salmonella enterica serovar Typhimurium decreases efp mRNA levels during course of infection. We determined that the decrease in efp mRNA is triggered by low levels of charged tRNA , a condition that Salmonella experiences when inside a macrophage phagosome. Surprisingly, downregulation of EF-P selectively promotes expression of the virulence mgtC gene and contributes to Salmonella's ability to survive inside macrophages. The decrease in EF-P levels induces ribosome stalling at the consecutive proline codons of the mgtP open reading frame in the mgtCBR leader RNA, and thus allows formation of a stem-loop structure promoting transcription of the mgtC gene. The substitution of proline codons in the mgtP gene eliminates EF-P-mediated mgtC expression and thus Salmonella's survival inside macrophages. Our findings indicate that Salmonella benefits virulence genes by decreasing EF-P levels and inducing the stringent response inside host.

Mg 2+ regulates transcription of mgtA in Salmonella Typhimurium via translation of proline codons during synthesis of the MgtL peptide

“…2). During the preparation of this article, it has also been reported that loss of EF-P resulted in a 13-fold increase in the accumulation of the mgtA mRNA in cells grown with 0.5 mM Mg 2+ , as measured with quantitative RT-PCR (22). The role of EF-P is unique in this regard, because mutations in the tufA, tufB, and lepA genes, which encode other EFs (23,24), did not have significant effects on the expression of mgtA (Fig.…”

Elongation factor P controls translation of the mgtA gene encoding a Mg2+ transporter during Salmonella infection

“…Depending on whether ribosome stalling promotes or inhibits the formation of the attenuator stem‐loop, it controls transcription elongation into the downstream genes and affects mRNA levels of those target genes. In the mgtCBR virulence operon from the intracellular pathogen Salmonella enterica serovar Typhimurium, EF‐P controls both transcription of the mgtCBR operon (Nam, Choi, Shin, & Lee, ) and translation of the mgtB gene encoding the MgtB Mg 2+ transporter located within the mgtCBR operon (Choi, Choi, et al., ). At the level of transcription, EF‐P controls transcription elongation into the mgtCBR operon via three consecutive proline codons at mgtP ORF in the leader RNA.…”

“…At the level of transcription, EF‐P controls transcription elongation into the mgtCBR operon via three consecutive proline codons at mgtP ORF in the leader RNA. Removal of EF‐P affects ribosome stalling at mgtP and thus increases mRNA levels of the mgtC and mgtB genes (Choi, Choi, et al., ; Nam et al., ). And substitution of the consecutive proline codons at mgtP eliminates the EF‐P‐mediated increase in mRNA levels of the mgtC and mgtB genes (Choi, Choi, et al., ; Nam et al., ).…”

“…Removal of EF‐P affects ribosome stalling at mgtP and thus increases mRNA levels of the mgtC and mgtB genes (Choi, Choi, et al., ; Nam et al., ). And substitution of the consecutive proline codons at mgtP eliminates the EF‐P‐mediated increase in mRNA levels of the mgtC and mgtB genes (Choi, Choi, et al., ; Nam et al., ). In addition to EF‐P's role in transcriptional control, EF‐P also controls translation of the mgtB gene via two consecutive proline codons located in the mgtB coding region (Choi, Choi, et al., ).…”

“…In this case, removal of EF‐P results in a decrease in protein levels of the MgtB Mg 2+ transporter and thus substitution of those two proline codons prevents the decrease in MgtB protein levels even in the absence of EF‐P (Choi, Choi, et al., ). Interestingly, given that mRNA levels of EF‐P decrease during Salmonella infection (Nam et al., ), Salmonella is likely to produce an altered ratio of the MgtC virulence protein to the MgtB Mg 2+ transporter (Choi, Choi, et al., ), which is required for Salmonella pathogenesis (Choi, Choi, et al., ; Lee & Groisman, ).…”