database uses EG10826 for recD. Finally, ECK numbers are specifically used for alleles in the MG1655 strain of E. coli K-12. Complete lists of genes and their synonyms can be obtained from databases such as EcoGene or Uniprot. Proteomics Proteome The genome sequence of E. coli predicts 4288 protein-coding genes, of which 38 percent initially had no attributed function. Comparison with five other sequenced microbes reveals ubiquitous as well as narrowly distributed gene families; many families of similar genes within E. coli are also evident. The largest family of paralogous proteins contains 80 ABC transporters. The genome as a whole is strikingly organized with respect to the local direction of replication; guanines, oligonucleotides possibly related to replication and recombination, and most genes are so oriented. The genome also contains insertion sequence (IS) elements, phage remnants, and many other patches of unusual composition indicating genome plasticity through horizontal transfer. Several studies have experimentally investigated the proteome of E. coli. By 2006, 1,627 (38%) of the predicted proteins (open reading frames, ORFs) had been identified experimentally. Mateus et al. 2020 detected 2,586 proteins with at least 2 peptides (60% of all proteins). Post-translational modifications (PTMs) Although much fewer bacterial proteins seem to have post-translational modifications (PTMs) compared to eukaryotic proteins, a substantial number of proteins are modified in E. coli. For instance, Potel et al. (2018) found 227 phosphoproteins of which 173 were phosphorylated on histidine. Interestingly, the majority of phosphorylated amino acids were serine (1,220 sites) with only 246 sites on histidine and 501 phosphorylated threonines and 162 tyrosines. Interactome The interactome of E. coli has been studied by affinity purification and mass spectrometry (AP/MS) and by analyzing the binary interactions among its proteins. Protein complexes. A 2006 study purified 4,339 proteins from cultures of strain K-12 and found interacting partners for 2,667 proteins, many of which had unknown functions at the time. A 2009 study found 5,993 interactions between proteins of the same E. coli strain, though these data showed little overlap with those of the 2006 publication. Binary interactions. Rajagopala et al. (2014) have carried out systematic yeast two-hybrid screens with most E. coli proteins, and found a total of 2,234 protein-protein interactions. This study also integrated genetic interactions and protein structures and mapped 458 interactions within 227 protein complexes. Normal microbiota E. coli belongs to a group of bacteria informally known as coliforms that are found in the