Mutations that alter the transport function of the lamB protein in Escherichia coli

Abstract

Some E. coli K-12 lamB mutants, those producing reduced amounts of LamB protein (one-tenth the wild type amount), grow normally on dextrins but transport maltose when present at a concentration of 1 μM at about one-tenth the normal rate, lamB Dex- mutants were found as derivatives of these strains. These Dex- mutants are considerably impaired in the transport of maltose at low concentrations (below 10 μM), and they have a structurally altered LamB protein which is impaired in its interaction with phages λ and K10 but still interacts with a λ host range mutant λhh*. The Dex- mutants are double lamB mutants carrying one mutation, already present in the parental strains, that reduces LamB synthesis and a second that alters LamB structure. The secondary mutations, present in different independent Dex- mutants, are clustered in the same region of the lamB gene. Dex+ revertants were isolated and analyzed: when the altered LamB protein is made in wild-type amount, due to a reversion of the first mutation, the phenotype reverts to Dex+. However, these Dex+ revertants are still very significantly impaired in maltose transport at low concentrations (below 10 μM).