Identification of a cytoplasmic membrane-associated component of the maltose transport system of Escherichia coli.

The maltose transport system of Escherichia coli contains at least five components, three of which, i.e. the products of lamB, malE, and malF genes, have so far been identified as constituents of the outer membrane, periplasmic space, and cytoplasmic membrane, respectively. We identified another component, a cytoplasmic membrane protein of an apparent molecular weight of 43,000, as the product of the malK gene on the basis of polyacrylamide gel electrophoretic analysis of various mutants and suppressed strains and by the incorporation of extra tyrosine residue into this proten in malK amber mutants containing the suppressor Su3+ allele. The transport of maltose thus appears to require at least two proteins associated with the cytoplasmic membrane.