The root-knot nematode resistance gene (Mi) in tomato: construction of a molecular linkage map and identification of dominant cDNA markers in resistant genotypes

A dominant allele at the Mi locus on chromosome 6 of tomato (Lycopersicon esculentum Mill) confers resistance to three species of root-knot nematodes (Meloidogyne). The resistance, which is associated with a localized necrotic response, was originally introduced into tomato from the wild species Lycopersicon peruvianum. As a step towards the molecular cloning of Mi, we have identified closely linked DNA markers from both cDNA and genomic DNA libraries as restriction fragment length polymorphisms (RFLPs). DNA from tomato populations segregating for nematode resistance was analyzed to generate a high-resolution genetic map of this region. Additional information on gene order was obtained by comparing the size of the introgressed L. peruvianum chromosomal segment within a collection of nematode-resistant tomato lines. Among the four cDNA markers that are tightly linked to Mi, three are dominant, i.e. L. peruvianum-specific. One cDNA marker corresponds to a gene family comprising 20-30 members, one of which is diagnostic for all nematode-resistant genotypes tested. The presence of non-homologous sequences around the Mi gene may contribute to the suppression of recombination in this region of the genome in crosses heterozygous for Mi. The potential of 'walking' from closely linked markers to Mi is discussed.     

Experimental documentation of natural hybridization inCactaceae: Origin of Lloyd's Hedgehog Cactus,Echinocereus ×lloydii

The origin ofEchinocereus ×lloydii Britt. & Rose, pro sp. (Lloyd's Hedgehog Cactus) was investigated using comparative morphology, cytology, biochemistry, and particularly, artificial hybridization. Numerous artificial crosses between the putative parentsE. coccineus Engelm. (a species of claret-up cactus) andE. dasyacanthus Engelm. (Texas Rainbow Cactus) were successful, resulting in the production of hundreds of seeds with hybrid embryos. The F₁ hybrid progeny (i.e., syntheticE. ×lloydii) grew to sexual maturity in about four and one-half years, whereupon successful backcrosses and F₂ generation hybrids were also obtained. The known F₁ hybrids closely approximated naturalE. ×lloydii. The fertility of these syntheticE. ×lloydii was high, like their natural counterparts. The populations ofE. ×lloydii in Pecos County, Texas are inferred to have originated as the result of natural interspecific hybridization. It is assumed thatE. ×lloydii or similar plants may arise wherever the parental taxa grow sympatrically.     

Temporal genetic variation in a population of the pocket gopher,Geomys bursarius

Genetic variation at eight polymorphic loci was examined in a population of a subterranean rodent, the plains pocket gopher (Geomys bursarius), sampled over a 10-yr period. Two loci exhibited relatively minor changes in gene frequencies, while the remaining loci demonstrated major shifts in predominant alleles, loss of minor alleles, and addition of alleles due to migration. Significant deviations from Hardy-Weinberg expectations, concomitant to heterozygote deficiencies, were observed for several loci. Temporal heterogeneity, as measured by F_ST, was high and comparable to that exhibited by local populations sampled over relatively short periods of time. The high degree of temporal genetic variation is consistent with observations that fossorial rodents occur in locally isolated populations with small effective population sizes that are subject to genetic drift, bottlenecking, and inbreeding.     

Activation of calpain I and calpain II: a comparative study using terbium as a fluorescent probe for calcium-binding sites

The present study demonstrates the activation of calpain I and calpain II by micromolar levels of terbium and has utilized the enhancement in the fluorescence of protein-bound terbium to study and compare the calcium binding sites of the two enzymes. Calpain I and calpain II were isolated from bovine erythrocytes and brain, respectively. While the rates of activation of calpain I by terbium and calcium are comparable, the rate of activation of calpain II was much greater in the presence of terbium than in the presence of calcium. Binding of terbium ions to calpains was monitored by the enhanced terbium fluorescence and by the changes in the intrinsic protein fluorescence of calpains. Stoichiometric titrations indicated that calpain I and calpain II bound four and six molar equivalents of terbium ion, respectively. During the titration, the intrinsic protein fluorescence of calpain II was successively quenched whereas that of calpain I showed an abrupt drop just prior to the saturation. The association constants (Ka) increased from 10(5) to 10(7) M-1 for calpain I and from 10(4) to 10(6) M-1 for calpain II with addition of increasing molar equivalents of terbium. Titration of enzymatic activities with calcium showed that the activation of calpain I required fewer molar equivalents of metal ions than were necessary for the activation of calpain II, in agreement with stoichiometric titration with terbium.     

Macromolecular crowding extends the range of conditions under which DNA polymerase is functional

The nick-translation reaction of E. coli DNA polymerase I (Pol I) was used as a model system to demonstrate the ability of macromolecular crowding to alter the response of an enzyme to a number of basic parameters, such as pH, temperature or inhibitors. In the presence of high concentrations of non-specific polymers, nick translation occurred under a variety of otherwise strongly inhibitory conditions. The conditions tested included a range of pH values or temperatures or inhibitory concentrations of urea, formamide or ethidium bromide. These crowding effects are accentuated at higher ionic strengths, suggesting their origin in increased binding between the polymerase and its DNA template-primer under crowded conditions. Kinetic measurements were consistent with such a mechanism.     

Clustering of phosphorylated amino acid residues in neurofilament proteins as revealed by 31P NMR

The state of phosphorylation in neurofilament (NF) proteins is studied by the 31P NMR technique. The 31P NMR spectrum of intact NF proteins at pH 7.0 is comprised of a major resonance at 4.18 ppm and a minor resonance at 3.53 ppm. The chemical shifts of the major and minor resonances are strongly dependent on pH and have pKa values for phosphoserine of 5.85 and for phosphothreonine of 6.00, respectively. 31P NMR spectra of isolated NF polypeptides show nonequivalent phosphoserine clusters in NF150 and in NF200. Their chemical shifts are very similar in both polypeptides, but the intensities of homologous resonances are different. NF68 has no detectable 31P resonance signal. Phosphate-specific monoclonal antibodies to NF200 can distinguish phosphates of various clusters. Microtubule proteins can also produce specific alteration of the 31P resonances of NF200. NF proteins digested by calcium-activated neutral protease (CANP) show relatively little change in 31P resonances.     

An assay for inhibitors of nucleoside transport based upon the use of 5-[125I]iodo-2'-deoxyuridine as permeant

5-[125I]Iodo-2'-deoxyuridine (IdUrd) has been shown to serve as a permeant for the nucleoside transport system of human erythrocytes and to be matabolically inert in these cells. Linear initial velocities were obtained at 20 degrees C for 125IdUrd transport, yielding a Km of 73 +/- 18 microM (n = 6). Low-affinity inhibitors of 125IdUrd transport, such as adenosine (Ki = 32 +/- 2 microM, n = 2), could be characterized by Michaelis-Menten kinetics. However, high-affinity inhibitors, such as 6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine, caused nonlinear initial velocities when added to the cells simultaneously with 125IdUrd. Conditions were defined (viz., 20-min pretreatment of cells with test compound followed by 5.0-min incubation with 1.0 microM 125IdUrd, all at 20 degrees C) whereby high-affinity inhibitors of IdUrd transport can be identified and evaluated according to their 50% inhibitory concentrations. The use of 125IdUrd as permeant greatly expedites the testing of compounds as inhibitors of nucleoside transport by allowing the cell pellets generated in these assays to be monitored directly in a gamma spectrometer, thereby circumventing the solubilization and decolorization of cell pellets required by assays that use 3H- or 14C-labeled nucleoside permeants.     

Human endothelial cells inhibit granulocyte aggregation in vitro

Granulocyte aggregation in response to circulating or locally released inflammatory mediators may cause vascular injury. The factors that regulate the granulocyte aggregation response and prevent its occurrence are not defined. We found that primary monolayers of human endothelial cells (EC) derived from umbilical veins released products that inhibited granulocyte aggregation. When polymorphonuclear leukocytes (PMN) and EC were incubated together, the subsequent aggregation response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) was inhibited by 40 to 60%, depending in part on the duration of incubation and the concentration of the agonist. Suspension of the granulocytes in albumin-containing buffer that had been rocked with EC monolayers had a similar effect, demonstrating that the EC release a soluble product that modulates the aggregation response. The fMLP concentration-response curve was shifted downward and to the right by EC. Incubation of the granulocytes with endothelial monolayers for various times indicated that the inhibition was maximal at 2 to 3 min, and the PMN responsiveness returned to control over the next 15 min. The inhibiting effect was not selectively directed against fMLP, because incubation of PMN with EC or suspending the PMN in supernatants from endothelial monolayers also inhibited aggregation stimulated by platelet-activating factor, leukotriene B4, and C5a desarg. Release of the inhibitory activity by EC was attenuated by indomethacin, suggesting that the activity is in part due to a cyclooxygenase pathway product. Prostacyclin (PGI2), an eicosanoid produced by EC via the cyclooxygenase pathway, inhibited granulocyte aggregation; however, PGI2 was much less potent as an inhibitor of PMN aggregation than of platelet aggregation. Furthermore, the concentration of PGI2 in buffer that had been incubated with EC was not sufficient to account for the magnitude of the PMN inhibition. The concentration of prostaglandin E2 (PGE2) was also insufficient to completely account for the inhibition. EC that had been treated with indomethacin or aspirin, which blocked the release of PGI2 and PGE2, retained the partial ability to release an activity that blunted granulocyte aggregation; this inhibiting activity was stable at 37 degrees C for 60 min. The results indicate that human EC have the biologic potential to modulate granulocyte aggregation stimulated by inflammatory mediators, and the activity is only partly due to PGI2 and other cyclooxygenase products of arachidonic acid.(ABSTRACT TRUNCATED AT 400 WORDS)     

von Willebrand factor. A reduced and alkylated 52/48-kDa fragment beginning at amino acid residue 449 contains the domain interacting with platelet glycoprotein Ib

We have purified a reduced and alkylated tryptic fragment of von Willebrand factor (vWF) which migrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 52/48-kDa doublet, but behaved as a single 46-kDa species after partial deglycosylation. After extensive treatment with denaturants, the 52/48-kDa polypeptide retained its ability to inhibit ristocetin-induced platelet aggregation in the presence of native vWF, as well as aggregation induced by desialylated vWF alone. Therefore, the 52/48-kDa polypeptide interacts with the platelet glycoprotein Ib receptor even in the absence of ristocetin. Both the 52/48- and the 46-kDa species inhibited ristocetin-induced binding of the intact molecule to platelets, but did not affect thrombin-induced binding. Determination of the NH2-terminal sequence of both members of the doublet gave identical results: VTLNPSDPEHCQ. This provided additional evidence that differences between the doublet constituents were only of carbohydrate composition and established the position of this peptide within the vWF polypeptide chain of approximately 2050 amino acid residues as beginning with the residue tentatively designated 449. These studies suggest that native conformation is not necessary for binding of vWF to platelets at the glycoprotein Ib receptor and that a linear amino acid sequence following residue 449 defines a domain responsible for this interaction.     

An Immunoblot Study of Neurofilament Degradation In Situ and During Calcium-Activated Proteolysis

The degradation of neurofilament (NF) proteins was examined by immunoblot methods to identify, characterize, and monitor the appearance of immunoreactive breakdown products during the loss of NF triplet proteins. Individual NF proteins and their breakdown products were identified using polyclonal and monoclonal antibodies to NF proteins. NF degradation was compared during calcium-activated proteolysis of isolated rat NF, during an experimental influx of calcium into excised rat spinal nerve roots, and during NF breakdown in transected rat peripheral nerve. These different experimental conditions produced similar patterns of NF fragmentation, including the transient appearance of NF immunobands between Mr 150,000-200,000 and 110,000-120,000 as well as the appearance and accumulation of NF immunobands between Mr 45,000 and 65,000. Most immunoreactive NF fragments remained Triton-insoluble. Low levels of the same immunoreactive fragments were present in control neural tissues, suggesting that calcium-activated proteolysis may be operative in the turnover and/or processing of NF proteins in vivo. Very similar patterns of NF degradation during experimental calcium influxes into different CNS and PNS tissues are indicative of the widespread distribution of calcium-activated NF protease in neural tissues.