A genetic approach to defining the sites of interaction of a membrane protein with different external agents.

In addition to a role in maintaining outer membrane structural integrity, the OmpA protein of Escherichia coli serves as a receptor for different phages, is required in the recipient cell for efficient conjugation, and functions in the internalization of receptor-bound colicins. To determine whether the same or different sites of OmpA protein are needed for these different functions, this paper presents the properties of a collection of ompA mutants selected as being defective in phage receptor function, but containing normal amounts of OmpA protein. Of 44 mutants examined, most were affected in more than one OmpA protein function, showing that there is considerable overlap in sites needed for different functions. The pattern of this overlap can be represented in a phenotypic map of OmpA protein functions.