Using Codon Usage to Predict Genes Origin: Is the Escherichia coli Outer Membrane a Patchwork of Products from Different Genomes?

Analysis of the codon usage of genes coding for the structuralcomponents of the outer membrane in Escherichia coli, is consistentwith the requirement for high expression of these genes. Becauseporins (which constitute the major protein component of theouter membrane), and LPS (which constitute the major outermostconstituent of the outer membrane), are synthesized from genesdisplaying widely different codon usage, it is possible to investigatethe origin of the outer membrane. The analysis predicts thatthe outer membrane might originate from a genome other thanthe genome coding for the major part of the cell. Such a specialorigin would explain in structural terms, the likely lethalityof porins if they were inadvertently inserted within the innermembrane, giving rise to the Gram-negative bacterial type, havingan envelope comprising two membranes, instead of a single cytoplasmicmembrane and a murein sacculus.