Bacteriophage P22 as a vehicle for transducing cosmid gene banks between smooth strains of Salmonella typhimurium: use in identifying a role for aroD in attenuating virulent Salmonella strains

Summary A cosmid gene bank of the virulent Salmonella typhimurium C5 was constructed in Escherichia coli K12. The bank was repackaged into bacteriophage heads and transduced into the semi-rough S. typhimurium strain AS68 which expresses the LamB receptor protein. Approximately 6000 ampicillin-resistant transductants were pooled and used as host for the propagation of bacteriophage P22. The P22 lysate was able to transduce cosmid recombinants to smooth strains of S. typhimurium and individual transductants were selected which complemented various S. typhimurium auxotrophic mutations. A stable mutation was introduced into the aroD gene of S. typhimurium C5. The resulting aroD ^- mutant, named CU038, was highly attenuated compared with the wild-type parent strain and BALB/c mice immunised orally with CU038 were well protected against challenge with the virulent C5 parental strain. Using the cosmid bank repackaged into bacteriophage P22 heads it was possible to isolate cosmid recombinants that could complement the aroD mutation of CU038 either by in vitro selection using minimal medium or in vivo selection for restoration of virulence in BALB/c mice. Repackaged P22 cosmid banks could provide a simple system for selecting in vivo for Salmonella virulence determinants. A Salmonella typhi strain harbouring mutations in aroA and aroD was constructed for potential use as a live oral typhoid vaccine in humans.     

The endogenous lectins of the chick blastoderm are present in association with an apolipoprotein in distinct organelles and in the extracellular matrix

Summary Affinity purified preparations of the galactose-binding lectin from gastrulating chick blastoderms consist of three main polypeptides. Two of these have been identified as the 14 kD and 16 kD galactose-binding lectins. A third one migrates in SDS-PAGE gels with a relative molecular weight of 6,500±500 and has been identified as an apolipoprotein (Apo) of plasma very low density lipoproteins, Apo-VLDL-II. We have studied the localization of these polypeptides using immunofluorescence and ultrastructural immunocytochemistry with peroxidase and protein-A gold. The 14 kD lectin occurs in the intracellular yolk where it is mainly present within the electron lucent component. The 16 kD is also present in the intracellular yolk platelets, but tends to predominate in the electron-dense component. In addition, the 16 kD lectin is also present in pleiomorphic yolk-associated organelles and in the extracellular matrix. Apo-VLDL-II is also localized in the electron-lucent component of the yolk platelet and in the extracellular matrix. Our results suggest that the lectin(s) are associated with Apo-VLDL-II in the yolk platelet, and may subsequently become externalized.     

Temporal relationship between nerve-stump-length-dependent changes in the autophosphorylation of a cyclic AMP-dependent protein kinase and the acetylcholine receptor content in skeletal muscle

The acetylcholine receptor (AChR) content and the autorphosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II (R-II) were evaluated in rat soleus muscles at 24, 30 and 66 hr after surgical denervation by cutting the nerve at a short distance (short-nerve-stump) and at a long distance (long-nerve-stump) from the muscle. AChR content was based on the specific binding of [¹²⁵I]alpha-bungarotoxin (BUTX); changes in the autophosphorylation of R-II were based upon the predominant in vitro³²P-phosphorylation of a 56-Kd soluble protein in cytosolic fractions of solei. The AChR content and the³²P-autophosphorylation of R-II were increased in samples from short-nerve-stump solei, but not from long-nerve-stump solei, after a denervation-time of 30 hr. This nerve-stump-length dependency indicates that the two denervation effects are not related to the immediate halt of impulse-evoked muscle contractility. Furthermore, the results show that alterations in the³²P-autophosphorylation of R-II occurred before, as well as whenever, increases in the AChR content were found. Speculatively, this temporal relationship may be significant with respect to the potential role of R-II in gene expression.Abbreviations ACh acetylcholine - AChR acetylcholine receptor(s) - BUTX alpha-bungarotoxin - Kd kilodalton - PAGE polyacrylamide gel electrophoresis - R-II regulatory subunit of cyclic AMP-dependent protein kinase type II - SDS sodium dodecyl sulfate     

Spontaneous abortion and confined chromosomal mosaicism

Summary Confined placental chorionic mosaicism is reported in 2% of viable pregnancies cytogenetically analyzed on chorionic villi samplings (CVS) at 9–12 weeks of gestation. In follow-up studies this mosaicism has been shown to be associated with increased frequency of second and third trimester pregnancy loss or intrauterine fetal growth retardation. We have studied 54 spontaneous abortions (SA) for the detection of confined placental mosaicism and found 11 of them to be mosaic. All mosaic cases were identified among first trimester spontaneous abortions, and the mosaicism was confined to specific placental or embryonic/fetal cell lineages. These results indicate that the previously reported mosaicism in SA represents both confined and generalized types of mosaicism and that its accepted frequency of 5%–10% in SA will likely be higher. Over the whole gestational period, the confined placental mosaicism is more common than the reported rate of 1%–2% seen in viable pregnancies at CVS, and a higher proportion of pregnancy complications than previously suspected may be associated with confined placental mosaicism.     

Synthesis of the biologically active β-subunit of human nerve growth factor in Escherichia coli

The gene(NGFB) encoding the β subunit of mature human nerve growth factor (hNGFB) was subcloned into the pJLA503 expression vector under the control of bacteriophage promoters p_R and p_L, and expressed in Escherichia coli. The recombinant protein represented approximately 3% of the total cellular protein. Biologically active hNGFB was solubilized (0.2% total NGFB) and purified by cation-exchange chromatography and it yielded two bands on polyacrylamide-gel electrophoresis under nonreducing conditions, corresponding to the monomeric (14 kDa) and homodimeric (26.5 kDa) forms of the molecule. Both hNGFB forms were immunopositive on Western blots with rabbit anti-NGFB antibodies; however, following additional purification, only the species corresponding to the hNGFB homodimer was biologically active on cultured chicken dorsal root ganglion neurons. These results demonstrate the feasibility of synthesizing the biologically active form of hNGFB in E. coli.     

gltF, a member of the gltBDF operon of Escherichia coli, is involved in nitrogen-regulated gene expression

We report here the construction and analysis of insertional mutations in each of the three genes of the gltBDF operon and the nucleotide sequence of the region downstream from gltD. Two open reading frames were identified, the first of which corresponds to gltF. The gltB and gltD genes code for the large and small subunits, respectively, of the enzyme glutamate synthase (GOGAT). gltF codes for a protein, with a molecular mass of 26,350 Da, which is required for Ntr induction. Histidase synthesis was determined as a measure of Ntr function. First, insertions in gltB, gltD or gltF all prevent Ntr induction. Second, complementation analysis indicates that high-level expression of both the gltD and gltF genes is required for the induction of the Ntr enzymes under nitrogen-limiting conditions, indicating that the phenotype of the gltB insertion probably results from polarity on gltD and gltF. Third, glutamate-dependent repression of the glt operon appears to be mediated by the product of the gltF gene. Thus, the gltBDF operon of Escherichia coli is involved in induction of the so-called Ntr enzymes in response to nitrogen deprivation, as well as in glutamate biosynthesis.     

Isolation of a New Polysaccharide-Digesting Bacterium from a Salt Marsh

A new marine bacterium that digested a variety of storage and structural polysaccharides, including agar, was isolated. Strain 2-40 is a nonfermentative gram-negative, polarly flagellated rod that sometimes grew as a filamentous helix and secreted a melaninlike pigment. Its characteristics conform to those of no previously described species.     

Effects of Salicylate on Virus-Infected Tobacco Plants

Salicylate watered onto the soil of tobacco plants in pots reduced the antigen accumulation and local lesion growth of tobacco necrosis virus mechanically inoculated on the leaves. It also retarded the growth of the necrotic centres of lesions and, in parallel, inhibited ethylene production from infected leaves. However, the therapeutic index of salicylate was very small and the chemical had to be applied in advance of, or at the same time as virus inoculation to give good levels of resistance. The number of lesions and their rate of appearance were not affected by salicylate. In addition, it did not induce resistance against multiplication, systemic spread or symptom severity in tobacco plants inoculated with a necrotic strain of potato virus Y. These findings suggest that salicylate is not likely to prove useful as polyvalent chemotherapeutic agent.     

Protease activities in non-embryogenic and embryogenic carrot cell strains during callus growth and embryo formation

Embryogenic and non-embryogenic cell strains of Daucus carota L. were examined for their protease activity using a wide range of chromogenic synthetic peptides as substrates. High arginine-specific activity was present in all strains, but no protease activity "specific" for embryogenic or non-embryogenic strains could be detected with the substrates tested. The specific protease activity was 5–10 times higher in the non-embryogenic as compared to the embryogenic strain for most tested substrates, and this difference was not due to release of proteases in the latter. All strains showed a decrease in protease activity when cultured in media without 2,4-dichlorophenoxyacetic acid, but the embryos had high protease activity in comparison with the nondifferentiated cell aggregates. In the latter aggregates, hydrolyzing activity towards three of the substrates (H-D-Phe-Pip-Arg- p -nitroanilide, Suc-Ala-Pro-Phe- p -nitro-anilide and Bz-Phe-Val-Arg- p -nitroanilide) was absent, whereas the embryos were able to hydrolyze them.