Multifaceted stoichiometry control of bacterial operons revealed by data-independent acquisition mass spectrometry

More than half of the protein-coding genes in bacteria are organized in polycistronic operons composed of two or more genes. Whether the operon organization maintains the stoichiometric expression of the genes within an operon remain under debate. In this study, we performed a label-free data-independent acquisition hyper reaction monitoring mass-spectrometry (HRM-MS) experiment to quantify the Escherichia coli proteome in exponential phase and quantified 93.6% of the cytosolic proteins, covering 67.9% and 56.0% of the translating polycistronic operons in BW25113 and MG1655 strains, respectively. We found the shorter operons tend to be more tightly controlled for stoichiometry than longer operons, and those operons for metabolic pathways are less controlled for stoichiometry compared with operons for protein complexes, illustrating the multifaceted nature of the operon-wise regulation: the operon-wise unified transcriptional level and gene-specific translational level. This multi-level regulation benefits the host by optimizing the efficiency of the productivity of metabolic pathways and maintenance of different types of protein complexes. Overall design: RNA-seq and Ribo-seq of E. coli strain BW25113 in M9 minimal medium