Grad-seq shines light on unrecognized RNA and protein complexes in the model bacterium Escherichia coli

Stable protein complexes, including those formed with RNA, are major building blocks of every living cell. Escherichia coli has been the leading organism with respect to global bacterial protein-protein networks. However, there has been no global census of RNA/protein complexes in this model species of microbiology. Here, we performed Grad-seq to establish an RNA/protein complexome, reconstructing sedimentation profiles in a glycerol gradient for ~85% of all E. coli transcripts and ~49% of the proteins. In presenting use cases for this resource to be exploited, we show that its stable association with 30S ribosomes gives the seemingly noncoding RNA RyeG of prophage origin away as an mRNA of a toxic small protein. Similarly, we show that the broadly conserved uncharacterized protein YggL is a 50S subunit factor in assembled 70S ribosomes. Overall, this study complements existing interactome resources for the primary model bacterium E. coli with valuable RNA/protein complexome information and should facilitate functional discovery in this and many related species. 22 total RNA samples from E. coli wild type resolved on a glycerol gradient resulting in 20 fractions and a pellet fraction. A lysate sample is given as input control.