Architecture of the outer membrane of Escherichia coli K12. II. Freeze fractur morphology of wild type and mutant strains

Freeze fracturing electron microscopy of Escherichia coli K12 cells showed that the outer fracture face of the outer membrane is densily occupied with particles. On the inner fracture face of the outer membrane, pits are visible, which are probably complementary to the particles at opposite fracture face. This observation suggests that the particles are micelle-like. In some mutants which lack one or more major outer membrane proteins the density of particles is reduced. The loss of protein d appeared to a prerequisite for this phenomenon. However, mutants which lack all glucose and heptose-bound phosphate in their lipopolysaccharide also have a reduction in particle density whereas, the amount of protein d is normal. Moreover, loss of lipopolysaccharide by EDTA treatment also caused a reduction in the density of particles. From these results it is hypothesized that the particles consist of lipopolysaccharide aggregates stabilized by divalent cations and probably complexed with protein and/or phospholipid.     

Retinoic acid induces transglutaminase activity but inhibits cornification of cultured epidermal cells

In cultured mouse epidermal basal cells, retinoic acid is a potent inducer of transglutaminase, the enzyme responsible for isodipeptide bond formation in protein cross-linking in the production of the cornified membrane during terminal differentiation. Paradoxically retinoic acid also inhibits the formation of the cross-linked envelope and greatly reduces the level of dipeptide bond formation in epidermal cells induced to differentiate by calcium. These results suggest a novel mechanism by which retinoids can modify transglutaminase activity and epidermal differentiation.     

meoA is the structural gene for outer membrane protein c of Escherichia coli K12

Summary The isolation and characterization of two mutants of Escherichia coli K12 with an altered outer membrane protein c is described. The first mutant, strain CE1151, was isolated as a bacteriophage Mel resistant strain which contains normal levels of protein c. Mutant cells adsorbed the phage with a strongly decreased rate. Complexes of purified nonheat modified wild type protein c and wild type lipopolysaccharide inactivated phage Me1, indicating that these components are required for receptor activity for phage Me1. When wild type protein c was replaced by protein c of strain CE1151, the receptorcomplex was far less active, showing that protein c of strain CE1151 is altered. The second mutant produces a protein c with a decreased electrophoretic mobility, designated as protein c^*. An altered apparent molecular weight was also observed for one or more fragments obtained after fragmentation of the mutant protein with cyanogen bromide, trypsin and chymotrypsin. Alteration of protein c was not accompanied by a detectable alteration in protein b or its fragments. Both mutations are located at minute 48 of the Escherichia coli K12 linkage map. The results strongly suggest that meoA is the structural gene for protein c.     

Architecture of the Outer Membrane of Escherichia coli III. Protein-Lipopolysaccharide Complexes in Intramembraneous Particles

In a previous paper (A. Verkleij, L. van Alphen, J. Bijvelt, and B. Lugtenberg, Biochim. Biophys. Acta 466:269-282, 1977) we have hypothesized that particles on the outer fracture face of the outer membrane ([Formula: see text]), with corresponding pits on the inner fracture face of the outer membrane ([Formula: see text]), consist of lipopolysaccharide (LPS) aggregates stabilized by divalent cations and that they might contain protein and/or phospholipid. In the present paper the roles of LPS, cations, and proteins in these [Formula: see text] particles are described more extensively, using a strain that lacks the major outer membrane proteins, b, c, and d (b(-) c(-) d(-)), and has a reduction in the number of [Formula: see text] particles of 75%. To study the role of divalent cations in the formation of [Formula: see text] particles, these b(-) c(-) d(-) cells were grown or incubated with Ca(2+), Mg(2+), or putrescine. The presence of Ca(2+) resulted in the appearance of many [Formula: see text] particles and [Formula: see text] pits. Mg(2+) and putrescine were less effective than Ca(2+). Introduction of these particles was not accompanied by alterations in the relative amounts of LPS and cell envelope proteins. Ca(2+) treatment of a heptoseless derivative of a b(-) c(-) d(-) strain did not result in morphological changes. Incubation of Ca(2+)-treated cells with ethylenediaminetetraacetate caused the disappearance of the introduced particles as well as the release of more than 60% of the cellular LPS. These results strongly support the hypothesis that LPS is involved in the formation of [Formula: see text] particles and [Formula: see text] pits. The roles of various outer membrane proteins in the formation of [Formula: see text] particles were studied by comparing the freeze-fracture morphology of b(-) c(-) d(-) cells with that of cells which contain one of the outer membrane proteins b, c, d, and e or the receptor protein for bacteriophage lambda. The results showed that the presence of any of these five proteins in a b(-) c(-) d(-) background resulted in a large increase in the number of [Formula: see text] particles and [Formula: see text] pits, indicating that these proteins are, independent of each other, involved in the formation of [Formula: see text] particles and [Formula: see text] pits. The simplest explanation for the results is that in wild-type cells each particle consists of LPS complexed with some molecules of a single protein species, stabilized by either divalent cations or polyamines. It is hypothesized that the outer membrane of the wild-type cell contains a heterogeneous population of particles, of which 75% consists of protein b-LPS, protein c-LPS, and protein d-LPS particles. A function of these particles as aqueous pores is proposed.     

The two-step interaction between α-dimethylaminonaphthalene-1-sulfonyl-pepsinogen-(1–12) and pepsin

The binding between α-dimethylaminonaphthalenesulfonyl-(1–12) and porcine pepsin can be detected by the large changes that occur in the fluorescence spectra of the dimethylaminonaphthalenesulfonyl chromophore due to energy transfer from tryptophan residues of the protein. The interaction was previously shown to consist of two steps: a fast step leading to a greatly enhanced fluorescence followed by a slower rearrangement step which reduces the fluorescence but leads to tighter binding and inhibition of the catalytic activity of pepsin (1). The two steps have been studied over a wide range of values of pH, temperature, and ionic strength to gain additional insights into the physical events occurring during the interaction. Based on the pH and ionic strength dependence, the initial step most likely involves electrostatic interaction of the basic peptide inhibitor with the acidic surface of pepsin in a rapid collision process. The use of this fluorescent reporter group has also suggested that the equilibrium binding after the slower rearrangement may also be pH dependent with most effective binding at higher pH. The kinetics of the slow step were measured by monitoring the continuous fluorescence decay. The resulting rates are compared to the rates observed by others for binding of pepstatin to pepsin. From the pH dependence of fluorescence, pK_app values are obtained for the dansylated peptide (3.25), for the pH dependence of the initial binding step (4.87), and for the equilibrium position (4.75).     

Impact of salinity stress on soil-borne fungi of sugarbeet

The sugarbeet cultivar Kaumera was found to be highly susceptible to infection by the root-rot pathogens Rhizoctonia solani and Sclerotium rolfsii in the absence of salinity stress. Under this environmental condition, R. solani was more efficient than S. rolfsii in producing cell wall-degrading enzymes in infected hypocotyls. Xylanase and galactanase were most effective. The rate of cell wall degradation by R. solani was nearly 2.5 times that of S. rolfsii when cells walls of healthy hypocotyls were used as sole carbon substrate for the in vitro produced crude enzymes.Under salinity stress the pathogenicity and the performance of cell wall-degrading enzymes of R. solani and S. rolfsii varied profoundly. Pathogenicity studies showed that R. solani appeared to be more tolerant than S. rolfsii of the salinity stresses applied, and relatively more virulent to cv Kaumera. The activities of cell wall enzymes of R. solani decreased and those of S. rolfsii increased with increased salt concentration when cell wall material was used as a sole carbon source. The metabolic products produced under salinity stress by R. solani and R. solani in the cell wall amended culture media shifted the initial pH towards neutrality or slight alkalinity for R. solani and to high acidity for S. rolfsii.When model substrates were used, xyland and galactan were the most responsive substrates for degradation by the cell wall enzymes of the two fungi studied. The rate of degradation was higher for S. rolfsii than for R. solani. The excessive acidity in salt stressed S. rolfsii culture media suggested reduced activities of the enzymes involved in cell wall degradation in vivo. This may explain the decreased virulence potentialities.     

The recombination activating genes,RAG 1 and RAG 2, are on chromosome 11p in humans and chromosome 2p in mice

The recombination activating genes RAG-1 and RAG-2 are adjacent genes that act synergistically to activate variable-diversity-joining (V(D)J) recombination. Southern analysis of hybrid cell lines derived from patients with the Wilms tumor-aniridia-genitourinary defects-mental retardation (WAGR) syndrome and from mutagenized cell hybrids selected for deletions in chromosome 11 has allowed us to map the chromosomal location of the human RAG locus. The RAG locus defines a new interval of human chromosome 11p, but is not associated with any genetically mapped human disease. Guided by the chromosomal localization of the human recombination activating genes, we have also mapped the location of the mouse Rag locus.     

Use of Bioluminescence Markers To Detect Pseudomonas spp. in the Rhizosphere

The use of bioluminescence as a sensitive marker for detection of Pseudomonas spp. in the rhizosphere was investigated. Continuous expression of the luxCDABE genes, required for bioluminescence, was not detectable in the rhizosphere. However, when either a naphthalene-inducible luxCDABE construct or a constitutive luxAB construct (coding only for the luciferase) was introduced into the Pseudomonas cells, light emission could be initiated just prior to measurement by the addition of naphthalene or the substrate for luciferase, n-decyl aldehyde, respectively. These Pseudomonas cells could successfully be detected in the rhizosphere by using autophotography or optical fiber light measurement techniques. Detection required the presence of 10³ to 10⁴ CFU/cm of root, showing that the bioluminescence technique is at least 1,000-fold more sensitive than β-galactosidase-based systems.