O-antigen modifying operons in Salmonella bacterial and phage genome sequences. A. Examples of GtrABC operons. Operons are shown for phage ε34 and P22, as well as for a possibly intact P22-like prophage, which we call Scho1, in the genome of Salmonella enterica serovar Choleraesuis strain SC-B67 (where the putative gtrC gene is named SC0368); genes are indicated as colored rectangles, and rectangles of the same color are recognizably homologous to one another. The transcription of the P22 operon is indicated by a horizontal arrow. B. A CLUSTAL X2  generated neighbor-joining tree of fifty-one known Salmonella GtrC proteins. Horizontal distances in the tree are proportional to sequence differences, and bootstrap values (out of 1000 trials) are shown above the lines and sequence differences are shown below the lines for the long branches. Each GtrC protein is named on the right of the tree according to its location with its "phage" or "Salmonella serovar" name followed by and underlined space and the numeric portion of its GenBank "locus_tag"; "+ number" in parentheses indicates the number of additional identical sequences currently known in other Salmonella strains. On the far right, colored bars indicate the type of prophage that is associated with the gtrC gene; red, P22-like; yellow, P2-like; green, λ-like; and blue, prophage remnant of uncertain ancestry.