Structure and Synthesis of a Lipid‐Containing Bacteriophage

The lipid‐containing bacteriophage PM2 has four distinct structural proteins, as shown by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate or electrophoresis on cellulose acetate strips in the presence of 6–8 M urea. The molecular weights of these four polypeptides determined in several polyacrylamide gel systems are: I = 43000, II = 26000–27000, III = 12500, IV = 4700. The isoelectric points of the four viral proteins were determined on disrupted virus particles by electrophoresis on cellulose acetate strips in the presence of 6 M urea at various pH values. The mobilities were extrapolated to zero mobility, a method preferable to isoelectric focusing where the denatured viral proteins aggregate and precipitate near the isoelectric point. The method is well suited for the determination of the isoelectric point of proteins in the native or only partially denatured state. Whereas proteins I, III and IV have isoelectric points slightly under neutrality (pH 6.2, 5.8 and 5.5, respectively), the isoelectric point of protein II is around 12.3. Calcium ions are tightly bound to protein II. After removal of the calcium ions in the presence of 6 M guanidine hydrochloride and EDTA, the p I of protein II is 9. The isoelectric point of the intact virus, determined on cellulose strips, is around 7.3. Protein I, the spike protein, is the only structural polypeptide which is soluble in aqueous solutions around pH 7. All of the proteins are soluble in 6–8 M urea or 6 M guanidine hydrochloride at pH 7–8.5. Proteins III and IV, the nucleocapsid core proteins, have the solubility properties of proteolipids or highly lipophilic polypeptides as shown by their solubility in nonionic detergents and by their distribution in a Bligh and Dyer fractionation. Neither glycolipids nor glyco‐proteins are present in the virus. The distribution of phospholipids has been determined by chemical modification of the outer lamella or outer and inner lamellae of the bacteriophage lipid bilayer. The viral lipid bilayer is asymmetric; most of the phosphatidylglycerol residues form the outer lipid layer, most of the phosphatidylethanolamine residues the inner lipid layer. A complete model of the virus, including the assembly process, is discussed at the end of this report.