A SEQUENCE-SPECIFIC FUNCTION FOR THE N-TERMINAL SIGNAL-LIKE SEQUENCE OF THE TONB PROTEIN

TonB is a proline-rich protein which provides a functional link betwee n the inner and outer membranes of Gram-negative bacteria. TonB is anc hored to the inner membrane via an N-terminal signal-like sequence and spans the periplasm, interacting with transport receptors in the oute r membrane. We have investigated the role of the N-terminal signal-lik e peptide in TonB function. Replacement of the N-terminal sequence wit h heterologous sequences indicates that it has at least three distinct roles in TonB function: (i) to facilitate translocation of TonB acros s the cytoplasmic membrane; (ii) to anchor TonB to the cytoplasmic mem brane; (iii) a sequence-specific functional interaction with the ExbBD proteins.