A HYDROPHOBIC REGION OF RICIN-A-CHAIN WHICH MAY HAVE A ROLE IN MEMBRANE TRANSLOCATION CAN FUNCTION AS AN EFFICIENT NONCLEAVED SIGNAL PEPTIDE

Ricin A chain is a polypeptide of 267 amino acids containing a hydroph obic region near its carboxyl-terminus (residues 245-256) which has be en implicated in the membrane translocation step necessary for this ca talytically active toxin to reach its intracellular substrate. DNA fus ions were constructed that encoded hybrid proteins consisting of carbo xyl-terminal residues 233-267 or residues 238-267 of ricin A chain pre ceding mouse dihydrofolate reductase. When in vitro transcripts prepar ed from these constructs were translated in cell-free systems, the ric in A chain-derived sequences functioned as efficient signal peptides w hich directed dihydrofolate reductase into microsomes or into proteoli posomes containing microsomal membrane components. (C) 1995 Academic P ress, Inc.