Interrelationship of the phage λ receptor protein and maltose transport in mutants of Escherichia coli K12

Abstract

1. (1) The λ receptor protein in maltose-induced cells of Escherichia coli K12 is a major protein of the outer membrane and therefore amounts to about 100 000 copies per cell. 2. (2) 17 λ-resistant derivatives of the λ-sensitive strain E. coli W3110 were isolated independently; all were impaired in maltose transport and showed a much lower growth rate on maltotriose except one mutant, E. coli W3110/21 which resembled the wild type parent in that it grew equally fast on maltotriose and maltose. All mutants lacked the λ receptor protein. 3. (3) The presence of the maltose-inducible λ receptor protein in the missense mutant E. coli CR63 was demonstrated by SDS-gel electrophoresis of isolated outer membranes. The molecular weight of 47 000 daltons corresponded to the size of the wild type receptor protein. Four derivative strains with additional lamB mutations were obtained by selecting for mutants resistant to a λ phage with an extended host range (λh). They all grew equally fast on maltose and maltotriose but only one contained as much λ receptor protein as the original strain. There was no correlation between the amount of residual receptor protein in these mutants and the initial rate of transport which ranged from 13 to 47% of the transport rate of the parent strain E. coli CR63. 4. (4) Maltose-1-phosphate, trehalose, melibiose, sucrose, raffinose, and cellobiose at 2 mM up to 11 mM concentrations did not compete with maltose uptake. Growth of cells on trehalose of melibiose induced the maltose transport system to 20 or 7%, respectively, of the level observed in maltose-grown cells, measured as initial rate of maltose uptake.