Lysogenic conversion of Shigella flexneri type antigens was studied with the aid of wild-type and thermosensitive mutant phages. With all wild-type phages, the appearance of glucosylated antigen was accompanied by the appearance of polyprenyl phosphate glucose synthetase activity. With some of the mutant phages, the appearance of glucosylated antigen was not followed by the formation of lipid-linked glucose in the enzyme assay. The reverse has also been observed, i.e., the high rate of formation of lipid-linked glucose and the lack of V-type antigen.The 0-specific side chain of Shigella flexneri variant Y is composed of GlcNAc-Rha-Rha-Rha units. This structure determined the -, 3,4, or Y specificity (8,11). The serotypes la, 2a, 4a, 5, and variant X differ from variant Y in that they contain a-glucosyl residues attached to the GlcNAc-Rha-Rha-Rha primary chain (11). As in Salmonella (14), polyprenyl monophosphate glucose is involved in the formation of glucosylated 0 antigen in S. flexneri. The biosynthesis of this intermediate in vitro can be detected only in those strains of S. flexneri that contain glucosylated 0 antigen and can be estimated with the aid of polyprenyl phosphates prepared from plants (4). The type-specific antigens 1, II, IV, V, and the -7,8 antigen can be the result of lysogenic conversion (2,3,6,9,10).In the present work, we examined the synthesis of lipid-linked glucose in S. flexneri variant Y after lysogenization with different typeantigen-converting phages. The isolation of thermosensitive nonconverting mutants of the PE5 phage (6) was performed, and the biosynthesis of lipid intermediate catalyzed by cell envelope preparation of Shigella strains lysogenic for these mutants was assayed.School, Pecs, Hungary. Bacteriophages /1 and 4IV,, which convert the I and IV antigens, respectively, were obtained from S. Iseki; phages fV and f7,8, which convert the V and -7,8 antigens, respectively, were from G. Giammanco, and phages P90 and PE5, which convert the IV and V antigens, respectively, were isolated in the Institute of Microbiology, Pecs, Hungary.Microbiological technique. L agar plates contained L broth (10 g of tryptone, 5 g of yeast extract, and 5 g of NaCl in 1 liter of distilled water, adjusted to pH 7.2 with 1 M NaOH) and 1.5% agar (14). For obtaining bacterial mass, L broth was used which contained casein hydrolysate (POCH, Gliwice, Poland) instead of tryptone. Phage assays were carried out on overlay of L broth containing 0.6% of agar (1).Sera. S. flexneri type-and group-specific sera were obtained from State Institute of Hygiene, Warsaw, Poland, or prepared at the Institute of Microbiology, Pecs, Hungary. Antiphage serum was prepared as described by Adams (1). It had velocity constant K = 103.Isolation of thermosensitive nonconverting mutants of PE5 phage. Because of the lack of an appropriate selective procedure, hydroxylamine mutagenesis was performed by a slightly modified version of the Tessman procedure (12). After 72 h of mutagenic treatment with 0.4 M hydroxylamine in 0.1 M ph...