Escherichia coli gene products: Physiological functions and common ancestries

Knowledge about Escherichia coli genes, their gene products, and their roles in cell physiology has reached a point that invites a look at the horizon. We can look at what we know today and see it in a context of some kind of totality of knowledge about E. coli genes and their gene products that will be reached in time. Assembled here is a table of E. coli K-12 genes whose gene products are known, organized by principal physiological function, with literature references through most of 1994. We have summarized the distribution of gene products among physiological and functional categories. Also assembled is information on the amino acid sequence relatedness of E. coli proteins and classification of the functional relatedness of sequence-related pairs. These results are interpreted in the context of evolution, with the objective of understanding more about how genes evolve and ultimately of identifying the relatively small numbers of unique ancestral sequences that probably have generated the families of sequences we observe in E. coli today. We also present a compilation of multiple enzymes present in E. coli that carry out the same biochemical reaction. Some multiple enzymes are related by sequence and thus are likely to have descended from a common ancestor, but others have no apparent sequence relationship and may have derived from different ancestral sequences independently by convergent evolution, or they may have been acquired from another source by lateral transmission. We discuss the capacity for these multiple enzymes to serve as a rich resource that contributes significantly to the adaptive capability of E. coli.