Prophages integrating into prophages: A mechanism to accumulate type III secretion effector genes and duplicate Shiga toxin-encoding prophages in Escherichia coli

Bacteriophages (or phages) play major roles in the evolution of bacterial pathogens via horizontal gene transfer. Multiple phages are often integrated in a host chromosome as prophages, not only carrying various novel virulence-related genetic determinants into host bacteria but also providing various possibilities for prophage-prophage interactions in bacterial cells. In particular, Escherichia coli strains such as Shiga toxin (Stx)-producing E. coli (STEC) and enteropathogenic E. coli (EPEC) strains have acquired more than 10 prophages (up to 21 prophages), many of which encode type III secretion system (T3SS) effector gene clusters. In these strains, some prophages are present at a single locus in tandem, which is usually interpreted as the integration of phages that use the same attachment (att) sequence. Here, we present phages integrating into T3SS effector gene cluster-associated loci in prophages, which are widely distributed in STEC and EPEC. Some of the phages integrated into prophages are Stx-encoding phages (Stx phages) and have induced the duplication of Stx phages in a single cell. The identified attB sequences in prophage genomes are apparently derived from host chromosomes. In addition, two or three different attB sequences are present in some prophages, which results in the generation of prophage clusters in various complex configurations. These phages integrating into prophages represent a medically and biologically important type of inter-phage interaction that promotes the accumulation of T3SS effector genes in STEC and EPEC, the duplication of Stx phages in STEC, and the conversion of EPEC to STEC and that may be distributed in other types of E. coli strains as well as other prophage-rich bacterial species.     

Characterization of translucent segments observed in an smbA mutant of Escherichia coli

Abstract The smbA gene of Escherichia coli is essential for cell proliferation. The smbA2 mutant shows cold-sensitive colony formation at 22°C. A novel morphological phenotype, formation of a translucent segment at midcell or at a cell pole, was observed by phase-contrastt microscopy at a high frequency in the smbA2 mutant cells incubated in L medium lacking NaCl at 22°C, but not observed in L medium containing 1% NaCl or 20% sucrose at the same temperature. No translucent segment was observed in the wild-type cells in any of the media used. Electron microscopic observation revealed that the translucent segments resulted from the enlargement of a periplasmic space by separation of the inner membrane from the peptidoglycan layer and the outer membrane.     

Light-Induced Changes of Electrical Potential in Pulvinar Motor Cells of Phaseolus vulgaris L.

The sealing-off phenomenon of microelectrode tips has oftenbeen observed in plant cells during potential measurements.In motor cells of pulvinus, changes of the sealing-off potentialwere induced by blue light. These light-induced changes of electricalpotential were in the direction opposite to those of the changesin intracellular potential. The results were evaluated and discussedin relation to the changes of the potential difference of themotor cells and turgor movements of the pulvinus. (Received February 2, 1987; Accepted June 29, 1987)     

Immunohistochemical techniques for detection of dermatan sulfate proteoglycan in tissue sections

Dermatan sulfate proteoglycan chains were detected in tissue sections treated with chondroitin B-lyase (0.01 units/ml) in 20 mM Tris-HCl (pH 8.0) for 1 hr, followed by staining with antibody 9A2 specific for unsaturated uronic acid coupled to N-acetylgalactosamine-4 sulfate. In contrast, after treatment with chondroitin B-lyase, no positive staining was observed with antibodies 3B3 and 1B5 which react to the unsaturated uronic acid coupled to N-acetylgalactosamine 6-sulfate and unsaturated uronic acid coupled to N-acetylgalactosamine, respectively. The distribution of dermatan sulfate thus revealed was confirmed by comparison with that found by monoclonal antibody 6B6 which reacts with small proteoglycans carrying dermatan sulfate side chains. The localization of positive staining in fibrous connective tissues was almost identical with these two procedures.     

Development of nephrotic ICGN mice--the origin, reproductive ability, and incidence of glomerulonephritis

ICGN is a strain of spontaneous nephrotic mice with nonproliferative glomerular lesions. It was derived from an outbred Yok: ICR colony in our laboratory. The renal disease constantly occurred in animals of the first to the tenth generations (greater than 13.0%; 70 days of age). When affected males were mated with unaffected females, the incidence of the disease in their offspring was 38.8% (n = 49) at 70 days after birth. When both parents were affected, their offspring were all affected (n = 12). The disease evenly progressed in both sexes. It usually began 40 to 150 days after birth and death occurred within two months after onset. The animals usually showed sufficient reproductive ability as long as unaffected females were used for mating.     

Kinetic studies on the prenyl chain elongation by undecaprenyl diphosphate synthase with artificial substrate homologues

In the undecaprenyl diphosphate synthase reaction, an allylic substrate homologue, (2Z,6E,10E)-4-methyl-geranylgeranyl diphosphate was found to be a potent competitive inhibitor against the allylic primer, (2Z,6E,10E)-geranylgeranyl diphosphate. On the other hand, it acted as a strong noncompetitive inhibitor against isopentenyl diphosphate. On the basis of these facts, the topology of the substrate-binding sites as well as the reason why the synthase reaction with (E)-3-methyl-3-pentenyl diphosphate always stops completely at the first stage of condensation, yielding an allylic diphosphate with a methyl group at the 4-position, are discussed.     

Effect of streptozotocin-induced diabetes on the activity of 7 alpha-hydroxy-4-cholesten-3-one-specific 12 alpha-hydroxylase in rats

The activity of 12 alpha-hydroxylase in hepatic microsomes from normal, streptozotocin-induced diabetic, and insulin-treated diabetic rats was studied with 7 alpha-hydroxy-4-cholesten-3-one as a substrate. In the diabetic rats, the 12 alpha-hydroxylase activity was about 50% lower than in the normal rats. Treatment of the diabetics with insulin cancelled the reduction of the activity. These results show that an insulin-deficient state causes a paradoxical decrease in the activity of the key enzyme for cholic acid formation.     

Isolation and Characterization of a Photosystem II Core Complex Depleted in the 43 kDa-Chlorophyll-Binding Subunit

The photosystem II core complex purified from digitonin extractsof spinach chloroplasts was resolved into two chlorophyll-proteincomplexes by digitonin polyacrylamide gel electrophoresis aftertreatment with 1 M potassium thiocyanate. One of the chlorophyll-proteincomplexes resolved consisted of 47, 32, 30 and 9 kDa polypeptidesand the other was complementally composed of only the 43 kDapolypeptide. The former complex was highly active in the photoreductionof 2, 6-dichlorophenol indophenol by 1,5-diphenylcarbazide andretained all of the components responsible for the electrontransport from the secondary electron donor (Z) to the primaryelectron acceptor (Q_A). EPR signal II_fast and II_slow were alsopreserved in this complex although their hyperfine structureswere largely modified. The complex was estimated to contain1.8 molecules of plastoquinone A as well as 1.5, 3.7 and 3.9molecules of cytochrome b559, pheophytin and ß-carotene,respectively, per Q_A. These results indicate that potassiumthiocyanate specifically removes the 43 kDa polypeptide fromthe PS II core complex leaving the electron transport systemin an almost intact state. (Received June 17, 1987; Accepted October 23, 1987)