Classifying E. coli K12 transcription factors into three groups based on their conservation across E. coli K12 close and remote relatives. The first group of TFs includes TFs that appear in most of the 30 bacteria in our study ('widely present'). A TF was included in this group if it appears in at least 14 of the 15 Enterobacteriaceae and in at least 14 of the 15 non-Enterobacteriaceae genomes. The second group includes those TFs that are present in all closely related Enterobacteriaceae genomes and are absent only from the more distantly related non-Enterobacteriaceae organisms ('entero-present'). A TF was classified into this group if it was present in at least 14 of the 15 Enterobacteriaceae and was absent from two or more of the 15 non-Enterobacteriaceae. The last group includes those TFs that are absent from some of the most closely related Enterobacteriaceae. TFs were classified into this group if they are absent from at least two of the 15 Enterobacteriaceae ('entero-absent'). For each of the three groups, five examples of conservation patterns of TFs that would be classified into that group are illustrated. Yellow and purple boxes represent presence of a TF in Enterobacteriaceae and non-Enterobacteriaceae, respectively. Black boxes indicate absence of the TF from an organism. Each column illustrates an example of presence/absence pattern that would result in classification of a TF in one of the three classes.