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1.
Infection by pathogenic fungi involves breaching the outer layer of the host by either mechanical or enzymatic means. Subtilisin-like proteinases are considered to be important in the infection process of entomopathogenic, nematophagous, and mycoparasitic fungi. Little is known regarding the expression of such proteinases by plant pathogenic fungi. Magnaporthe poae, a fungal pathogen of Kentucky bluegrass, expressed a subtilisin-like proteinase, proteinase Mp1, in the infected roots. Antibody was produced against the purified enzyme. From immunoblot analysis, expression of the proteinase in infected roots correlated with increasing severity of disease symptoms. Sequence analysis of a genomic clone indicated proteinase Mp1 was homologous to other fungal subtilisin-like proteinases. DNA gel blot analysis indicated proteinase Mp1 was encoded by a small gene family. 相似文献
2.
The function of gamma-aminobutyric acid (GABA) receptors, which mediate transmembrane chloride flux, can be studied by use of 36Cl- isotope tracer with membrane from mammalian brain by quench-flow technique, with reaction times that allow resolution of the receptor desensitization rates from the ion flux rates. The rates of chloride exchange into the vesicles in the absence and presence of GABA were characterized with membrane from rat cerebral cortex. Unspecific 36Cl- influx was completed in three phases of ca. 3% (t 1/2 = 0.6 s), 56% (t 1/2 = 82 s), and 41% (t 1/2 = 23 min). GABA-mediated, specific chloride exchange occurred with 6.5% of the total vesicular internal volume. The GABA-dependent 36Cl- influx proceeded in two phases, each progressively slowed by desensitization. The measurements supported the presence of two distinguishable active GABA receptors on the same membrane mediating chloride exchange into the vesicles with initial first-order rate constants of 9.5 s-1 and 2.3 s-1 and desensitizing with first-order rate constants of 21 s-1 and 1.4 s-1, respectively, at saturation. The half-response concentrations were similar for both receptors, 150 microM and 114 microM GABA for desensitization and 105 microM and 82 microM for chloride exchange, for the faster and slower desensitizing receptors, respectively. The two receptors were present in the activity ratio of ca. 4/1, similar to the ratio of "low-affinity" to "high-affinity" GABA sites found in ligand binding experiments. The desensitization rates have a different dependence on GABA concentration than the channel-opening equilibria.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
A survey for malic enzyme (Me) in laboratory strains of species A and species B of Anopheles culicifacies had uncovered two electrophoretic variants, slow and fast, in two strains of species B. Genetic analysis revealed the two variants to be codominant alleles segregating at a locus, Me, which is sex linked. Because of the XX-XY sex determining mechanism, in F1 females, two electromorphs, viz., slow and fast, were observed, whereas in males only one electromorph of maternal origin was seen. Linkage experiments with another X-linked mutant, white eye (w), indicated the map distance between the two loci to be 9.52 +/- 0.86. 相似文献
4.
A site in a tRNA precursor that can be processed by the whole RNase P enzyme but not by the RNA alone 总被引:1,自引:0,他引:1
A precursor molecule for 10 Sb RNA, the RNA moiety of the RNA processing enzyme RNase P, was purified, characterized for enzymatic activity, and compared to 10 Sb RNA and to RNase P. In these studies the K RNA, a dimeric precursor of tRNAGln-tRNALeu, coded by bacteriophage T4, was used as a substrate. This precursor contains two RNase P cleavage sites, one at each 5' end of the two tRNAs. The precursor 10 Sb and 10 Sb RNAs have the capacity to cleave the precursor tRNA molecule but only at the 5' end of tRNALeu, not at the 5' end of tRNAGln. Even when a substrate was prepared that contained only one site for RNase P (the one next to tRNAGln), this substrate was not cleaved by the RNA alone while the whole enzyme was effective in processing this substrate. The possible function of the protein of RNase P in the enzymatic reaction is discussed. 相似文献
5.
A murine monoclonal antibody (MAb), 2D8, was used in immunofluorescence reactions to detect respiratory syncytial virus (RSV) antigen in clinical specimens. Nasopharyngeal epithelial cells from 63 of 66 children with RSV infections reacted with this MAb. The MAb was further characterized and was demonstrated to recognize a conformational epitope on the dimer of the fusion protein of RSV. No reaction was detected with the MAb, 2D8, on Western blots of antigen prepared from RSV-infected HEp-2 cells under reducing conditions. Under non-reducing conditions, 2D8 reacted with a 145-170 K protein; this reactivity was lost when the antigen preparation was heated to 100 degrees C. 2D8 reacted with purified F glycoprotein of RSV Long in an ELISA, neutralized infectivity of RSV by >50% at a dilution of 1:500, and was able to inhibit cell-to-cell fusion of RSV-infected cells. In a competitive ELISA, the epitope detected by 2D8 was localized to antigenic site A. The conformational epitope detected by 2D8 required protein dimerization and glycosylation for full reactivity. This report extends previous characterizations of the F protein in its native state in that the MAb defines a conformational epitope on the fusion protein dimer that is expressed in natural infections and elicits antibody that can neutralize virus infectivity and inhibit cell-to-cell fusion. In addition to its application as a diagnostic reagent, this MAb can be of use in testing preparations of RSV or purified F protein in which the purification or extraction processes could have destroyed conformational epitopes. 相似文献
6.
The Weibull model is a flexible growth model that describes both general population growth and plant disease progress. However, lack of an asymptotic parameter has limited its wider application. In the present study, an asymptotic parameter K was introduced into the original Weibull model, written as; y = K {1 − exp [− ( t − a ) c ]}, in which a , b , c and K are location, scale, shape, and asymptotic parameters, respectively, y is the proportion of disease and t is time. A wide range of simulated disease progress data sets were generated using logistic, Gompertz and monomolecular models by specifying different parameter values, and fitted to both original and modified Weibull models. The modified model provided statistically better fits for all data than the original model. The modified model can thus improve the curve-fitting ability of the original model which often failed to converge, especially when the asymptote is less than 1.0. Actual disease progress data on wheat leaf rust and tomato root rot with different asymptotic values were also used to compare the original and modified Weibull models. The modified model provided a statistically better fit than the original model, and model estimates of asymptotic parameter K were nearly identical to the actual disease maxima reflecting the characteristics of the host-pathosystem. Comparison of logistic, Gompertz, and Weibull models including parameter K by fitting to the observed data on wheat leaf rust and tomato root rot revealed the applicability of the modified Weibull model, which in a majority of cases provided a statistically superior fit. 相似文献
7.
Segregation of Cytoplasmic Incompatibility Properties in CULEX PIPIENS FATIGANS 总被引:2,自引:2,他引:0
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Sarala K. Subbarao B. S. Krishnamurthy C. F. Curtis T. Adak R. K. Chandrahas 《Genetics》1977,87(2):381-390
Maternally inherited variants, which arose within a laboratory colony of Culex pipiens fatigans, have been studied by rearing cultures from single egg rafts. Segregation, i.e, variation of cytoplasmic incompatibility properties between the male progeny of individual females, was demonstrated. Also, from the daughters of individual females, sub-lines were derived within which all the males showed the same incompatibility or compatibility properties. Among the descendants of tetracycline-treated individuals were lines which superficially simulated these phenomena, but theses lines ultimately reverted to the cytoplasmic compatibility type of the strain which was submitted to the treatment. The types of variation s in cytoplasmic incompatibility properties that have been studied are discussed. 相似文献
8.
N Muthusamy A R Baluyut B Subbarao 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(8):2483-2492
The differential effect of cAMP on the regulation of early biochemical and cellular functions mediated through two different receptors on murine B cells are reported here. Surface IgM, the Ag receptor, and Lyb2, a 45-kDa differentiation Ag are concomitantly expressed on mature murine B lymphocytes. Triggering of B cells through these molecules, independently, resulted in inositol 1,4,5-triphosphate (IP3) generation, increase in intracellular Ca2+ levels, and cell enlargement associated with progression of cells from G0 to G1 ultimately resulting in DNA synthesis. Pretreatment of resting B cells with cholera toxin as well as other agents that raise the intracellular cAMP [(cAMP)i] such as forskolin, N6,2'-O-dibutyryl cyclic AMP, and 3-isobutyl-1 methyl xanthine inhibited the Ag receptor but not Lyb2-mediated DNA synthesis. The elevation of (cAMP)i inhibited the surface IgM but not Lyb2-mediated IP3 generation, Ca2+ response, and progression from G0 to G1 phase of the cell cycle. Failure of forskolin or N6,2'-O-dibutyryl cyclic AMP to inhibit Lyb2-mediated responses did not appear to be due to induction of cAMP-specific phosphodiesterase activity. Concentrations of H8 [N-(2-(methylamino)-ethyl)-5-isoquinoline sulfonamide, diHCl] inhibitory to cAMP dependent PKA prevented the inhibitory effect of forskolin on surface IgM-mediated Ca2+ response, suggesting that cAMP exerted its effects through PKA. These findings suggest that distinct PLC-coupled receptors, such as sIgM and Lyb2 molecules in B cells, may use either alternative mechanisms for phosphatidylinositol 4,5-bisphosphate hydrolysis or may use different intermediary transducer molecules that differ in their sensitivity to increased (cAMP)i levels. Thus "cross-talk" among cAMP and phosphatidylinositol signaling pathways was demonstrated for IgM but not Lyb2-mediated B cell activation. 相似文献
9.
Association of a pH-sensitive peptide with membrane vesicles: role of amino acid sequence 总被引:1,自引:0,他引:1
The solution properties and bilayer association of two synthetic 30 amino acid peptides, GALA and LAGA, have been investigated at pH 5 and 7.5. These peptides have the same amino acid composition and differ only in the positioning of glutamic acid and leucine residues which together compose 47% of each peptide. Both peptides undergo a similar coil to helix transition as the pH is lowered from 7.5 to 5.0. However, GALA forms an amphipathic alpha-helix whereas LAGA does not. As a result, GALA partitions into membranes to a greater extent than LAGA and can initiate leakage of vesicle contents and membrane fusion which LAGA cannot (Subbarao et al., 1987; Parente et al., 1988). Membrane association of the peptides has been studied in detail with large phosphatidylcholine vesicles. Direct binding measurements show a strong association of the peptide GALA to vesicles at pH 5 with an apparent Ka around 10(6). The single tryptophan residue in each peptide can be exploited to probe peptide motion and positioning within lipid bilayers. Anisotropy changes and the quenching of tryptophan fluorescence by brominated lipids in the presence of vesicles also indicate that GALA can interact with uncharged vesicles in a pH-dependent manner. By comparison to the peptide LAGA, the membrane association of GALA is shown to be due to the amphipathic nature of its alpha-helical conformation at pH 5. 相似文献
10.
ChunMei Yin JunJiao Li Dan Wang DanDan Zhang Jian Song ZhiQiang Kong BaoLi Wang XiaoPing Hu Steven J. Klosterman Krishna V. Subbarao JieYin Chen XiaoFeng Dai 《Molecular Plant Pathology》2022,23(8):1122
The arms race between fungal pathogens and plant hosts involves recognition of fungal effectors to induce host immunity. Although various fungal effectors have been identified, the effector functions of ribonucleases are largely unknown. Herein, we identified a ribonuclease secreted by Verticillium dahliae (VdRTX1) that translocates into the plant nucleus to modulate immunity. The activity of VdRTX1 causes hypersensitive response (HR)‐related cell death in Nicotiana benthamiana and cotton. VdRTX1 possesses a signal peptide but is unlikely to be an apoplastic effector because its nuclear localization in the plant is necessary for cell death induction. Knockout of VdRTX1 significantly enhanced V. dahliae virulence on tobacco while V. dahliae employs the known suppressor VdCBM1 to escape the immunity induced by VdRTX1. VdRTX1 homologs are widely distributed in fungi but transient expression of 24 homologs from other fungi did not yield cell death induction, suggesting that this function is specific to the VdRTX1 in V. dahliae. Expression of site‐directed mutants of VdRTX1 in N. benthamiana leaves revealed conserved ligand‐binding sites that are important for VdRTX1 function in inducing cell death. Thus, VdRTX1 functions as a unique HR‐inducing effector in V. dahliae that contributes to the activation of plant immunity. 相似文献