Technical Abstract: Phage vB_EcoM_CBA120 (CBA120) isolated against Escherichia coli O157:H7 from a cattle feedlot is morphologically very similar to the classic phage ViI of Salmonella enterica serovar Typhi. Until recently, little was known genetically or physiologically about the ViI-like phages, and non targeting E. coli had been described in the literature. The genome of CBA120 has been fully sequenced and is highly similar to those of ViI and of Shigella phage AG3. The core set of structural and replication-related proteins of CBA120 are homologous to those from T-even phages but more closely related to those from T4-like phages of Vibrio, Aeromonas, and cyanobacteria than others of enterobacteria. The baseplate and method of adhesion to the host are, however, very different from those of either T4 or the cyanophages. None of the outer baseplate proteins are conserved. Instead of T4's long and short tail fibers, CBA120, like ViI, encodes tail spikes related to those normally seen on podoviruses. The 158 kb genome, like that of T4, is circularly permuted and terminally redundant, but unlike T4, CBA120 does not substitute HMdC for cytosine in its DNA. However, in contrast to other coliphages, CBA120 and related coliphages we have isolated cannot incorporate 3H-thymidine (3H-dThd) into their DNA. Protein sequence comparisons cluster the putative "thymidylate synthase" of CBA120, ViI, and AG3 much more closely with those of Delftia phage fW-14, Bacillus subtilis phage, SP01, and Pseudomonas phage YuA, all known to produce and incorporate hydroxymethyluracil (HMdU).