THE PROTEIN TRANSLOCATION APPARATUS CONTRIBUTES TO DETERMINING THE TOPOLOGY OF AN INTEGRAL MEMBRANE-PROTEIN IN ESCHERICHIA-COLI

The assembly of integral membrane proteins is determined by features o f these proteins and the protein translocation apparatus, We used alka line phosphatase fusions to the membrane protein MalF to investigate t he role of the protein translocation machinery in the arrangement of p roteins in the cytoplasmic membrane of Escherichia coli. In particular , we studied the effects of prlA mutations on membrane protein topolog y, These mutations lie in the secY gene, which encodes a core componen t of the protein translocation apparatus, We find that the topology of some of the fusion proteins is changed and, in one case, is completel y inverted in prlA mutants, We discuss the mechanism of prlA-mediated export and the role of the protein translocation apparatus in contribu ting to membrane protein topology.