TRANSLOCATION OF N-TERMINAL TAILS ACROSS THE PLASMA-MEMBRANE

Previously we have shown that the first hydrophobic domain of leader p eptidase (lep) can function to translocate a short N-terminal 18 resid ue antigenic peptide from the phage Pf3 coat protein across the plasma membrane of Escherichia coli. We have now examined the mechanism of i nsertion of N-terminal periplasmic tails and have defined the features needed to translocate these regions. We find that short tails of up t o 38 residues are efficiently translocated in a SecA- and SecY-indepen dent manner while longer tails are very Poorly inserted. Efficient tra nslocation of a 138 residue tail is restored and is Sec-dependent by t he addition of a leader sequence to the N-terminus of the protein. We also find that while there is no amphiphilic helix requirement for N-t erminal translocation, there is a charge requirement that is needed wi thin the tail; an arginine and lysine residue can inhibit or completel y block translocation when introduced into the tail region. Intriguing ly, the membrane potential is required for insertion of a 38 residue t ail but not for a 23 residue tail.