Protein Ia and the lamB protein can replace each other in the constitution of an active receptor for the same coliphage.

Protein Ia and the lamB protein are both located in the outer membrane of Escherichia coli K-12. The lamB protein is known to be the receptor for phage lambda. Datta et al. [Datta, D. B., Arden, B. & Henning, U. (1977) J. Bacteriol. 131, 821--829] recently isolated a phage called TuIa that uses protein Ia for its adsorption. While phage TuIa fails to grow on ompB mutants, which lack protein Ia, we show here that host-range mutants of TuIa can be isolated that do grow on ompB strains. These host-range mutants fail to grow on ompB lamB double mutants, but retain the ability of the parental phage to grow on ompB+ lamB strains. They are therefore apparently able to use either protein Ia or the lamB protein for their adsorption. Genetic evidence suggests that essentially the same site on the lamB protein may be interacting with phage lambda or the host-range mutants of phage TuIa.