Identification of the phage gene for host receptor specificity by analyzing hybrid phages of T5 and BF23

The closely related coliphages T5 and BF23 differ in the receptor used for adsorption to cells. In order to identify phage genes encoding host receptor specificity, hybrid phages were isolated from crosses of T5 and BF23. These hybrid phages were analyzed for their protein composition, kinetics of adsorption to various bacterial strains, and DNA restriction maps. Analyses of the protein compositions of purified tails suggested that only one tail protein was involved in the expression of host specificity. In T5 tails this protein was identified as a minor tail protein of an apparent molecular weight of 67K. A corresponding BF23 protein could not be detected. The DNA region encoding structural proteins was analyzed by digestion with the restriction enzymes BamHI, HindIII, and PstI. The distribution of restriction sites in these recombinants implied that the region affecting host specificity was located at ca. 90% of the T5 genome length. Evidence is presented that this gene is identical to the oad gene previously described (K.J. Heller and D. Bryniok (1984), J. Virol. 49, 20-25). The location of other genes encoding tail proteins is discussed.