Autoregulation of the tufB operon in Salmonella

• Published in: Molecular microbiology 2016-06, Vol.100 (6), p.1004-1016
• Main Authors: Brandis, Gerrit, Bergman, Jessica M., Hughes, Diarmaid
• Format: Article
• Language: English
• Subjects: Bacterial Proteins; Biologi med inriktning mot mikrobiologi; Biology with specialization in Microbiology; EF-Tu; Escherichia coli - genetics; Escherichia coli - metabolism; Genes; Genes, Bacterial; Homeostasis; Microbiology; Mikrobiologi; Molecular Genetics; Molekylär genetik; Mutation; Operon; Peptide Elongation Factor Tu - genetics; Peptide Elongation Factor Tu - metabolism; Point Mutation; post-transcriptional regulation; Protein Biosynthesis; Rho; RNA, Bacterial - genetics; RNA, Bacterial - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Salmonella; Salmonella - genetics; Salmonella - metabolism; Salmonella enterica; Transcription, Genetic; tufA; tufB
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.13364

Summary In Salmonella enterica and related species, translation elongation factor EF‐Tu is encoded by two widely separated but near‐identical genes, tufA and tufB. Two thirds of EF‐Tu is expressed from tufA with the remaining one third coming from tufB. Inactivation of tufA is partly compensated by a doubling in the amount of EF‐TuB but the mechanism of this up‐regulation is unknown. By experimental evolution selecting for improved growth rate in a strain with an inactive tufA we selected six different noncoding or synonymous point mutations close to the tufB start codon. Based on these results we constructed a total of 161 different point mutations around the tufB start codon, as well as tufB 3′‐truncations, and measured tufB expression using tufB‐yfp transcriptional and translational fusions. The expression data support the presence of two competing stem‐loop structures that can form in the 5′‐end of the tufB mRNA. Formation of the ‘closed’ structure leads to Rho‐dependent transcriptional termination of the tufB mRNA. We propose a model in which translational speed is used as a sensor for EF‐Tu concentration and where the expression of tufB is post‐transcriptionally regulated. This model describes for the first time how expression of the most abundant Salmonella protein is autoregulated. The amount of EF‐Tu expressed from tufB can vary two‐fold but the mechanism of this regulation is unknown. Based on analysis of selected and constructed mutations, and using transcriptional and translational fusions, we propose a model where translational speed is used as a sensor for EF‐Tu concentration and where the expression of tufB is post‐transcriptionally regulated. This model describes for the first time how expression of the most abundant Salmonella protein is autoregulated.