Mutations in gene lamB: studies on structure and topology of an E. coli outer membrane protein

Results obtained in E. coli with a set of mutations conferring tight resistance to phage lambda lead to a first identification of three residues in the lamB protein which are important for adsorption of phage lambda. Residues 151 and 382 are important for reversible adsorption while residue 401 is important for irreversible adsorption. The identification of such residues may help to identify portions of the protein located at the cell surface. Assays of lambda receptor activity in merodiploid strains heterogenote for gene lamB show that the mutations studied can have a negative dominant effect. For one class of mutations (class II) this can be interpreted by negative complementation at the level of oligomerisation. The data confirm then that active lambda receptor is a trimer.