A helix stop signal in the isolated S-peptide of ribonuclease A

The isolated S-peptide (residues 1-20 of ribonuclease A) is known to show partial alpha-helix formation in aqueous solutions at low temperatures. We show here that the helix is limited to certain residues, including ones that are helical in the intact protein, and that a functional helix termination signal exists in the isolated peptide.