title: Mutations that alter the transport function of the LamB protein in Escherichia coli.
abstract: Some Escherichia 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 microM 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 microM), and they have a structurally altered LamB protein which is impaired in its interaction with phages lambda and K10 but still interacts with a lambda host range mutant lambda hh*. 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 microM).
mesh_terms: D001425:Bacterial Outer Membrane Proteins; D010582:Bacteriophage lambda / Q000378:metabolism*; D001692:Biological Transport; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005838:Genotype; D007700:Kinetics; D008320:Maltose / Q000378:metabolism; D009154:Mutation; D018272:Porins; D011991:Receptors, Virus / Q000235:genetics* / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D018272:Porins; D011991:Receptors, Virus; C016532:maltoporins; D008320:Maltose