The mycorrhizal colonization of six wetland plant species at sites differing in land use history

 Five wetland prairie sites and six native plant species in western Oregon were examined to determine patterns of vesicular-arbuscular mycorrhizal fungal (VAMF) colonization. The sites differed in type and intensity of past land use. VAMF colonization was tested in situ on seedlings from both field-sown seeds and from transplants. Colonization was measured as the percentage of root length with arbuscles or vesicles. All species (Deschampsia cespitosa, Downingia elegans, Eriophyllum lanatum, Hordeum brachyantherum, Microseris laciniata, and Plagiobothrys figuratus) became colonized by VAMF during the study. This is the first report of mycorrhizal colonization of these important native species. All sites supported mycorrhizal colonization of some of the experimental species. Average VAMF colonization ranged from 58% to 92% but was unrelated to subjective rankings of land use intensity. These results suggest that VAMF inoculum at all sites was sufficient to support revegetation by at least some species of native plants. Accepted: 16 September 1999     

A versatile system for the expression of nonmodified bacteriocins in Escherichia coli

AIMS: To develop a method and plasmid vectors suitable for expression of class II bacteriocins from Escherichia coli. METHODS AND RESULTS: The expression vector pSuV1 was constructed by inserting the PelB secretion signal coding sequence and a number of restriction endonuclease sites for cloning, into pTYB1. Codon optimized genes encoding the active mature region of each bacteriocin were constructed and inserted into pSuV1. Transfer of these constructs to a host expressing T7 RNA polymerase allowed for expression of secreted mature or fusion forms of the bacteriocins. Generation of the fusion, to the adjacent intein-chitin-binding domain gene, was achieved by removal of a small intervening BseRI fragment. The bacteriocins BacR1, divercin V41, enterocin P, pediocin PA-1 and piscicolin 126 were expressed from this system. For piscicolin 126, expression levels of 200 microg l(-1) in the mature form and 1100 microg l(-1) when cleaved from the fusion partner were achieved. All expressed bacteriocins displayed antimicrobial activity. CONCLUSIONS: Several class II bacteriocins have been expressed in E. coli using purpose designed plasmid vectors described here. SIGNIFICANCE AND IMPACT OF THE STUDY: This method provides a common expression system capable of producing a range of different class II bacteriocins. It allows researchers to study class II bacteriocins without access to the original producer strain, the native bacteriocin gene, or highly specific heterologous producing strains. Resulting expression levels are as high or higher than those previously reported for related bacteriocins.     

The Epstein-Barr virus protein, latent membrane protein 2A, co-opts tyrosine kinases used by the T cell receptor

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis and is associated with several human malignancies. The EBV protein latent membrane protein 2A (LMP2A) promotes viral latency in memory B cells by interfering with B cell receptor signaling and provides a survival signal for mature B cells that have lost expression of surface immunoglobulin. The latter function has suggested that LMP2A may enhance the survival of EBV-positive tumors. EBV is associated with several T cell malignancies and, since LMP2A has been detected in several of these disorders, we examined the ability of LMP2A to transmit signals and interfere with T cell receptor signaling in T cells. We show that LMP2A is tyrosine-phosphorylated in Jurkat TAg T cells, which requires expression of the Src family tyrosine kinases, Lck and Fyn. Lck and Fyn are recruited to the tyrosine-phosphorylated Tyr112 site in LMP2A, whereas phosphorylation of an ITAM motif in LMP2A creates a binding site for the ZAP-70/Syk tyrosine kinases. LMP2A also associates through its two PPPPY motifs with AIP4, a NEDD4 family E3 ubiquitin ligase; this interaction results in ubiquitylation of LMP2A and serves to regulate the stability of LMP2A and LMP2A-kinase complexes. Furthermore, stable expression of LMP2A in Jurkat T cells down-regulated T cell receptor levels and attenuated T cell receptor signaling. Thus, through recruiting tyrosine kinases involved in T cell receptor activation, LMP2A may provide a survival signal for EBV-positive T cell tumors, whereas LMP2A-associated NEDD4 E3 ligases probably titer the strength of this signal.     

Allosteric modulation of ligand binding to low density lipoprotein receptor-related protein by the receptor-associated protein requires critical lysine residues within its carboxyl-terminal domain

The low density lipoprotein receptor-related protein (LRP) is a large endocytic receptor that recognizes more than 30 different ligands and plays important roles in protease and lipoprotein catabolism. Ligand binding to newly synthesized LRP is modulated by the receptor-associated protein (RAP), an endoplasmic reticulum-resident protein that functions as a molecular chaperone and prevents ligands from associating with LRP via an allosteric-type mechanism. RAP is a multidomain protein that contains two independent LRP binding sites, one located at the amino-terminal portion of the molecule and the other at the carboxyl-terminal portion of the molecule. The objective of the present investigation was to gain insight into how these two regions of RAP interact with LRP and function to modulate its ligand binding properties. These objectives were accomplished by random mutagenesis of RAP, which identified two critical lysine residues, Lys-256 and Lys-270, within the carboxyl-terminal domain that are necessary for binding of this region of RAP to LRP and to heparin. RAP molecules in which either of these two lysine residues was mutated still bound LRP but with reduced affinity. Furthermore, the mutant RAPs were significantly impaired in their ability to inhibit alpha(2)M* binding to LRP via allosteric mechanisms. In contrast, the mutant RAP molecules were still effective at inhibiting uPA.PAI-1 binding to LRP. These results confirm that both LRP binding sites within RAP cooperate to inhibit ligand binding via an allosteric mechanism.     

Q & A. Philip Ingham

Philip Ingham grew up in Liverpool and graduated from Cambridge University in 1977. He did his D.Phil in Developmental Genetics at Sussex University and postdoctoral work in Strasbourg, France before joining the laboratory of David Ish-Horowicz at the ICRF Mill Hill Laboratories. Here he applied the emerging technique of tissue in situ hybridisation to the analysis of the Drosophila segmentation genes. After a short spell at the MRC Laboratory of Molecular Biology in Cambridge, he rejoined the ICRF as a Research Scientist at the Developmental Biology Unit in Oxford. His group pioneered the analysis of the Hedgehog signalling pathway in Drosophila and in collaboration with the labs of Andy McMahon and Cliff Tabin at Harvard University, discovered the Hedgehog gene family in vertebrates. In 1996 he was appointed Professor of Developmental Genetics at the University of Sheffield where he has established the Centre for Developmental Genetics.     

Inactivation of dispatched 1 by the chameleon mutation disrupts Hedgehog signalling in the zebrafish embryo

Searches of zebrafish EST and whole genome shotgun sequence databases for sequences encoding the sterol-sensing domain (SSD) protein motif identified two sets of DNA sequences with significant homology to the Drosophila dispatched gene required for release of secreted Hedgehog protein. Using morpholino antisense oligonucleotides, we found that inhibition of one of these genes, designated Disp1, results in a phenotype similar to that of the "you-type" mutants, previously implicated in signalling by Hedgehog proteins in the zebrafish embryo. Injection of disp1 mRNA into embryos homozygous for one such mutation, chameleon (con) results in rescue of the mutant phenotype. Radiation hybrid mapping localised disp1 to the same region of LG20 to which the con mutation was mapped by meiotic recombination analysis. Sequence analysis of disp1 cDNA derived from homozygous con mutant embryos revealed that both mutant alleles are associated with premature termination codons in the disp1 coding sequence. By analysing the expression of markers of specific cell types in the neural tube, pancreas and myotome of con mutant and Disp1 morphant embryos, we conclude that Disp1 activity is essential for the secretion of lipid-modified Hh proteins from midline structures.     

Interaction of Staphylococcus aureus fibronectin-binding protein with fibronectin: affinity, stoichiometry, and modular requirements

The repetitive D1, D2, and D3 elements of Staphylococcus aureus fibronectin-binding protein FnBPA each bind the N-terminal 29-kDa fragment (N29) of fibronectin with low micromolar dissociation constants (Kd), but in tandem they compose a high affinity domain, D1-3. An additional seven Fn-binding segments have been predicted in FnBPA in a region N-terminal of the D-repeats (Schwarz-Linek, U., Werner, J. M., Pickford, A. R., Gurusiddappa, S., Kim, J. H., Pilka, E. S., Briggs, J. A., Gough, T. S., Hook, M., Campbell, I. D., and Potts, J. R. (2003) Nature 423, 177-181). We have evaluated the requirements for high affinity binding of N29 to the D-repeat domain and determined the affinity and stoichiometry of N29 binding to segments that are N-terminal of the D-repeats in the related FnBPB adhesin. We confirmed that D1-3 has two equivalent high affinity sites (Kd, approximately 1 nm) and provided evidence for one or more lower affinity sites (Kd, approximately 0.5 microm). Bimodular D1-2 and D2-3 exhibit intermediate affinity sites with respective Kd values of 0.25 and 0.044 microm, as well as a low affinity site with a Kd value of 2.2-2.5 microm. We also identified two binding domains that are N-terminal of the D-repeats, designated DuB and DuA. Segments internal to these domains individually bound N29 with similar Kd values of approximately 2 microm, whereas the DuBA polypeptide possessing both segments and other intervening sites bound four molecules of N29 with much higher affinity (Kd, approximately 10 nm). DuBAD, a larger polypeptide harboring all of the known or predicted binding motifs in FnBPB, bound seven to eight molecules of N29, with a Kd of approximately 7 nm. Because most of the isolated binding segments display low affinity for N29 and lack motifs for binding of one or both of the 1F1 and 5F1 modules in the N-terminal domain of Fn, we propose that high affinity is achieved in part as a consequence of self-interaction between bound molecules of N29.