Structure and synthesis of a lipid-containing bacteriophage. Amphiphilic properties of protein IV of bacteriophage PM2.

Abstract

Interactions between lipids and the DNA-binding protein (protein IV) purified from bacteriophage PM2 were studied in vitro. The efficiency of incorporation of protein IV into single-walled liposomes was more than 90%. Protein IV embedded in liposomes interacted more strongly with PM2 DNA than protein IV alone. The DNA--protein-IV--liposome complex was relatively stable as observed by sedimentation behavior on a sucrose gradient. The interaction between DNA and the protein-IV--liposome was abolished by tryptic digestion, even though 40% of the protein remained in the vesicle. More than 70% of the amino acids of this embedded peptide segment were hydrophobic. Carboxypeptidase digestion of the protein-IV--liposome caused a release of 20% of the radioactivity of the vesicle without changing the DNA-binding ability of the complexes. Modification of the protein-IV--liposome with the chemical probe, 2,4-dinitrofluorobenzene, and analysis of the tryptic peptides released from the protein-IV--liposome demonstrated that the N-terminal basic amino acid cluster segment responsible for the DNA binding was located on the outer surface of the bilayer. These results support an earlier model in which protein IV anchors itself in the inner leaflet of the PM2 bilayer membrane, interacting with the DNA in the virion.