SecB dependence of an exported protein is a continuum influenced by the characteristics of the signal peptide or early mature region

We have used Escherichia coli alkaline phosphatase to show the interplay am ong the characteristics of two amino-terminal domains in the preprotein (th e signal peptide and the early mature region), the efficiency with which th is protein is transported, and its requirement for SecB to accomplish the t ransport process. The results suggest that although alkaline phosphatase do es not normally require SecB for transport, it is inherently able to utiliz e SecB, and it does so when its ability to interface,vith the transport mac hinery is compromised.