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P Maillot-Vernier H Schaller P Benveniste G Belliard 《Biochemical and biophysical research communications》1989,165(1):125-130
We report here, for the first time, the biochemical characterization of a plant mutant impaired in sterol biosynthesis. A fertile plant was regenerated from a tobacco callus resistant to LAB170250F, a potent inhibitor of the cytochrome-P450-obtusifoliol-14-demthylase. The resistant callus and the leaves from the regenerated plant are characterized by profound qualitative and quantitative changes in their sterol content. Self-fertilization of this plant yielded seeds with the same biochemical features, indicating that the new phenotype is of mutational origin. 相似文献
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haemolysin of Escherichia coli: Comparison of pore-forming properties between chromosome and plasmid-encoded haemolysins 总被引:3,自引:0,他引:3
Roland Benz reas Döbereiner Albrecht Ludwig Werner Goebel 《FEMS microbiology letters》1992,105(1-3):55-62
Abstract Lipid bilayer experiments were performed with chromosome-encoded haemolysin of Escherichia coli . The addition of the toxin to the aqueous phase bathing lipid bilayer membranes of asolectin resulted in the formation of transient ion-permeable channels with two states at small transmembrane voltages. One is prestate (single-channel conductance 40 pS in 0.15 M KCl) of the open state, which had a single-channel conductance of 420 pS in 0.15 M KCl and a mean lifetime of 30 s. Membranes formed of pure lipids were rather inactive targets for this haemolysin. Experiments with different salts suggested that the haemolysin channel was highly cation-selective at neutral pH. The mobility sequence of the cations in the channel was similar if not identical to their mobility sequence in the aqueous phase. The single-channel data were consistent with a wide, water-filled channel with an estimated minimal diameter of about 1 nm. The pore-forming properties of chromosome-encoded haemolysin were compared with those of plasmid-encoded haemolysin. Both toxins share common features, oligomerize probably to form pores in lipid bilayer membranes. Both types of haemolysin channels have similar properties but different lifetimes. 相似文献
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Induction of epithelial tubular morphogenesis in vitro by fibroblast-derived soluble factors 总被引:34,自引:0,他引:34
We have designed an in vitro system in which Madin-Darby canine kidney (MDCK) epithelial cells are cocultured in collagen gels with fibroblasts under conditions precluding heterocellular contact. Using this experimental approach, we have obtained evidence that fibroblast-derived soluble factors play a crucial role in the control of epithelial morphogenesis. First, MDCK cells suspended alone in collagen gels form spherical cysts, whereas in the presence of fibroblasts they form branching tubules. Second, MDCK cells grown as a monolayer on fibroblast-containing collagen gels invade the underlying matrix, within which they form a network of tubules. Third, fibroblast-conditioned medium mimics the effects of coculture by eliciting tubulogenesis by MDCK cells. These results demonstrate the involvement of diffusible paracrine factors in morphogenetic epithelial-mesenchymal interactions and provide a strategy for their molecular characterization. 相似文献
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Pre-S1 antigens and antibodies early in the course of acute hepatitis B virus infection 总被引:24,自引:3,他引:21
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The presence of the two "large" surface proteins of hepatitis B virus (HBV), P39 and GP42 of pre-S1-hepatitis B surface antigen, was assayed in the serum of an experimentally infected chimpanzee by using antibodies to a pre-S1-specific fusion protein synthesized in Escherichia coli. The immune response to pre-S1-hepatitis B surface antigen was monitored by using the pre-S1 fusion protein as an antigen. pre-S1 proteins were detected in the serum early in the course of infection and prevailed as long as hepatitis B surface antigen did, together with hepatitis B e antigen and viral DNA. Thus, the pre-S1 antigen can be considered a novel diagnostic marker for acute HBV infection. Antibodies to pre-S1, both immunoglobulin M and G classes, were also detected early in infection, shortly after the appearance of the pre-S1 antigen, suggesting its strong immunogenicity in vivo. The anti-pre-S1 antibodies therefore also represent an early serological marker for acute HBV infection and, owing to their early appearance and persistence, may play a role in the neutralization of the virus. 相似文献
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Analysis of a tyrosine-specific protein kinase activity associated with the retroviral erbB oncogene product 总被引:2,自引:0,他引:2
The transforming protein erbB of avian erythroblastosis virus (AEV) has considerable sequence homology with the epidermal growth factor (EGF) and appears to represent a truncated form of this receptor. The sequence of the erbB gene is furthermore related to that of other viral transforming genes such as src, fps, yes or abl. The transforming proteins of these src-related oncogenes as well as receptors for EGF, platelet-derived growth factor (PDGF), and insulin are associated with tyrosine-specific protein kinases. It has been difficult to demonstrate this activity for the erbB protein. To analyze the erbB gene product, we prepared polyclonal antibodies against a bacterially expressed erbB DNA restriction fragment (BamHI/BamHI). The antiserum is shown to immunoprecipitate the erbB protein from AEV-transformed chicken fibroblasts and also recognizes the EGF receptor protein. Both proteins become phosphorylated in vitro on tyrosine residues upon the addition of [gamma-32P]ATP. The protein kinase activity is low compared to other oncogene-specific kinases. This is not due to kinase blocking by the serum, because erbB carboxyterminal synthetic peptide antibodies give rise to low levels of protein kinase activity as well indicating that this may be a characteristic property of erbB in vitro. 相似文献
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Translationally coupled initiation of protein synthesis in Bacillus subtilis. 总被引:10,自引:1,他引:9
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The neomycin phosphotransferase gene (neo) from Transposon Tn5 is active in Gram-negative bacteria but silent in B. subtilis since it lacks an appropriate ribosome binding site for Gram-positive bacteria. Neo translation could be reactivated by coupling its initiation to the translational termination of the highly expressed beta-lactamase gene (penP) from B. licheniformis. This initiation occurred at the authentic neo start codon. Its efficiency was independent of the nucleotide sequence 5 to the neo gene, but strongly affected by the distance between the termination and initiation codon. It was the highest if both codons overlapped in the sequence ATGA. In B. licheniformis, a translationally coupled neo gene was inducible expressed as the penP gene demonstrating the potential of the technique to monitor the activity of expression units for which no direct assays exists. 相似文献