Bacteriophage PR4 is a lipid-containing phage that infects Escherichia coli K-12. We have examined the molecular composition of homogeneous preparations of this phage with the following results. The genome is a linear double-stranded DNA molecule of 14,500 base pairs (Mr 9.6 × 106) having a GC content of 46%. The phage lipids are 98% (by weight) phospholipids and 2% neutral lipids. The phospholipids consist of 56% phosphatidylethanolamine, 37% phosphatidylglycerol, and 4.6% cardiolipin, by weight. The relative phosphatidylglycerol content of the phage phospholipids is twice that found in the host cell. The fatty acid compositions of the viral and cellular phospholipids are identical. The phage capsid contains 14 proteins ranging in molecular weight from 9000 to 60,000. The major capsid protein, comprising 80% of the total virion protein, has a molecular weight of 37,200. The purified phage contains 73% protein, 13% lipid, and 14% DNA (by weight) and has an isoelectric point of pH 4.2.
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