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SUMMARYBacteriophage ~W-I 4 is sensitive to osmotic shock. It contains sufficient free putrescine, 2-hydroxyputrescine and spermidine to neutralize about 15 ~o of the DNA phosphates. The ~-putrescinylthymine residues of the DNA could neutralize a further 25 ~o of the phosphates. Label is transferred from ornithine to the c~-putrescinyl residues of ~W-14 DNA. The rates of polyamine synthesis in Pseudomonas acidovorans are increased by ~W-I4 infection.The polyamines putrescine and spermidine are widespread in bacteria (Cohen I97I;Bachrach, 1973). They occur also in several Escherichia coli bacteriophages (Ames, Dubin & Rosenthal, I958; Ames & Dubin, 196o;Dion & Cohen, 1972; Fukuma & Cohen, 1973;Bachrach, Fischer & Klein, 1975). The capsids of the T-even phages behave like semipermeable membranes: the particles are osmotically fragile, and they retain their polyamines when dialysed against divalent cations such as Mg 2+ (Ames & Dubin, 196o Bacteriophage ¢W-I4 is structurally similar to the T-even phages (Kropinski & Warren I97o); however, it is unusual in that its DNA contains the hypermodified pyrimidine, ~-putrescinylthymine (Kropinski, Bose & Warren, I973). Its host, Pseudomonas acidovorans, contains much 2-hydroxyputrescine in addition to putrescine and spermidine (Karrer, Bose & Warren, I973). Unlike E. coli, P. acidovorans forms these polyamines from ornithine but not from arginine and is impermeable to putrescine (Karrer & Warren, 1974). This means that the polyamines of P. acidovorans can be labelled by use of radioactive ornithine or glutamate, but not by arginine or putrescine. Now we have determined the free polyamine content of ~W-~4 and have investigated, polyamine synthesis in ~5W-I4 infected bacteria.Pseudomonas acidovorans 29 was grown on casamino acids-mannitol (CAA-M; Kropinski et al. I973) for the preparation and titration of phage stocks and on tris-HCl-casamino acids-succinate (TCS; Lewis et al. I975) for the experiments. Growth was followed tnrbidimetrically. Cultures were always infected with a m.o.i, of IO at a density of 3 x lO 8 cells/ml.The preparation and titration of phage stocks have been described (Kropinski et aL 1973). Phage for analysis was purified by the method of Lewis et al. (i975), then dialysed exhaustively against dimethylglutarate buffer (Ames & Dubin, I96o).Phages were subjected to osmotic shock by suspending approximately equal numbers of p.f.u, of ~bW-x 4 and T4 in TN buffer (o.oI M-tris-HCl-o'I5 M-NaC1, pH 7"4) and in TN buffer containing 5 M-NaC1; after 20 h at room temperature, the TN suspension was diluted 2 2" 5 X IO n 38"8 0"094 28"6 I7'4 9"8Ioo-fold in TN; the TN/5 M-NaC1 suspension was diluted by a factor of lO 8 in distilled water and in 3 M-KC1. After 30 min at room temperature, the surviving phage were assayed for p.f.u, on P. acidovorans 29 and on E. coli B.The incorporation of radioactive putrescine by phage-infected cells was determined as described previously for uninfected cells (Karrer & Warren, I974)-Phage DNA was labelled by adding the appropriate ra...

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