Migration and differentiation of Nkx-2.2+ oligodendrocyte progenitors in embryonic chicken retina

During early neural development, the Nkx-2.2 homeobox gene is initially induced in the ventral ventricular zone of the central nervous system (CNS). At later stages, Nkx-2.2+ cells migrate away into the surrounding regions and co-express several oligodendrocyte marker genes. Here we report that Nkx-2.2+ cells also migrate into the avian retina from the optic nerve. These Nkx-2.2+ cells are specifically labeled by the early oligodendrocyte markers PDGFR alpha, O4 and GalC, but not the microglial marker QH1 or neuron-specific marker MAP-2. These observations provide further evidence that Nkx-2.2 is selectively expressed in migratory oligodendrocyte progenitor cells and that retina oligodendrocytes originate from the ventral diencephalon.

The highly recombinogenic bz locus lies in an unusually gene-rich region of the maize genome

The bronze (bz) locus exhibits the highest rate of recombination of any gene in higher plants. To investigate the possible basis of this high rate of recombination, we have analyzed the physical organization of the region around the bz locus. Two adjacent bacterial artificial chromosome clones, comprising a 240-kb contig centered around the Bz-McC allele, were isolated, and 60 kb of contiguous DNA spanning the two bacterial artificial chromosome clones was sequenced. We find that the bz locus lies in an unusually gene-rich region of the maize genome. Ten genes, at least eight of which are shown to be transcribed, are contained in a 32-kb stretch of DNA that is uninterrupted by retrotransposons. We have isolated nearly full length cDNAs corresponding to the five proximal genes in the cluster. The average intertranscript distance between them is just 1 kb, revealing a surprisingly compact packaging of adjacent genes in this part of the genome. At least 11 small insertions, including several previously described miniature inverted repeat transposable elements, were detected in the introns and 3' untranslated regions of genes and between genes. The gene-rich region is flanked at the proximal and distal ends by retrotransposon blocks. Thus, the maize genome appears to have scattered regions of high gene density similar to those found in other plants. The unusually high rate of intragenic recombination seen in bz may be related to the very high gene density of the region.

Control of oligodendrocyte differentiation by the Nkx2.2 homeodomain transcription factor

Oligodendrocytes are derived from glial precursors that arise from the ventral neural tube early in development. In the developing chicken CNS, oligodendrocyte progenitors selectively express Nkx2.2 homeodomain transcription factor, raising the possibility that Nkx2.2 may directly regulate oligogliogenesis. In this study, we have examined Nkx2.2 expression in rodent glial precursors and studied the effect of a loss of Nkx2.2 on oligodendrocyte and astrocyte differentiation. We show that Nkx2.2 is also expressed in mammalian oligodendrocyte progenitors and that the differentiation of MBP-positive and PLP-DM20-positive oligodendrocytes is dramatically retarded in Nkx2.2-null mutants along the entire rostrocaudal axis. In contrast, no effect is seen on astrocytic differentiation. Interestingly, absence of Nkx2.2 expression leads to a ventral expansion of the Olig1/Olig2 expression in neuroepithelial cells into the Nkx2.2 domain and a consequent increase in the production of Olig1/Olig2-positive and platelet-derived growth factor receptor α-positive oligodendrocyte progenitors. These results strongly suggest that Nkx2.2 regulates the differentiation and/or maturation, but not the initial specification, of oligodendrocyte progenitors. Consistent with this suggestion, overproduction of Nkx2.2 protein in fibroblast cells can induce gene expression from the proteolipid protein promoter.

Raf-1 promotes cell survival by antagonizing apoptosis signal-regulating kinase 1 through a MEK-ERK independent mechanism

The Ser/Thr kinase Raf-1 is a protooncogene product that is a central component in many signaling pathways involved in normal cell growth and oncogenic transformation. Upon activation, Raf-1 phosphorylates mitogen-activated protein kinase kinase (MEK), which in turn activates mitogen-activated protein kinase/extracellular signal-regulated kinases (MAPK/ERKs), leading to the propagation of signals. Depending on specific stimuli and cellular environment, the Raf-1--MEK--ERK cascade regulates diverse cellular processes such as proliferation, differentiation, and apoptosis. Here, we describe a MEK--ERK-independent prosurvival function of Raf-1. We found that Raf-1 interacts with the proapoptotic, stress-activated protein kinase ASK1 (apoptosis signal-regulating kinase 1) in vitro and in vivo. Deletion analysis localized the Raf-1 binding site to the N-terminal regulatory fragment of ASK1. This interaction allows Raf-1 to act independently of the MEK--ERK pathway to inhibit apoptosis. Furthermore, catalytically inactive forms of Raf-1 can mimic the wild-type effect, raising the possibility of a kinase-independent function of Raf-1. Thus, Raf-1 may promote cell survival through its protein-protein interactions in addition to its established MEK kinase function.

Mice lacking the Nkx6.2 (Gtx) homeodomain transcription factor develop and reproduce normally

The Nkx homeobox genes are expressed in a variety of developing tissues and have been implicated in controlling tissue patterning and cell differentiation. Expression of Nkx6.2 (Gtx) was previously observed in the embryonic neural tube, testis, and differentiating oligodendrocytes. To investigate the role of Nkx6.2 in the control of cell specification and differentiation, we generated mice with null mutations in Nkx6.2 using the standard gene targeting approach. Null mutant mice were viable and fertile without apparent histological and immunohistochemical changes in the central nervous systems and testis. The absence of detectable phenotypes suggests a redundant function of Nkx6.2 in mouse development.

The proapoptotic protein Bad binds the amphipathic groove of 14-3-3zeta

Through interaction with a multitude of target proteins, 14-3-3 proteins participate in the regulation of diverse cellular processes including apoptosis. These 14-3-3-interacting proteins include a proapoptotic Bcl-2 homolog, Bad (Bcl-2/Bcl-XL-associated death promoter). To understand how 14-3-3 interacts with Bad and modulates its function, we have identified structural elements of 14-3-3 necessary for 14-3-3/Bad association. 14-3-3 contains a conserved amphipathic groove that is required for binding to several of its ligands. We used peptides of known binding specificity as competitors to demonstrate that Bad interacts with 14-3-3zeta via its amphipathic groove. More detailed analysis revealed that several conserved residues in the groove, including Lys-49, Val-176, and Leu-220, were critical for Bad interaction. These results were applied to investigations of the ability of 14-3-3 to prevent Bad-induced cell death. When co-expressed with Akt, wild-type 14-3-3 could reduce the ability of Bad to cause death, however 14-3-3zetaK49E, which cannot bind Bad, failed to inhibit Bad. It seems that the amphipathic groove of 14-3-3 represents a general binding site for multiple ligands, raising issues related to competition of ligands for 14-3-3.

[Effect of wuzi yanzong pill and its disassembled prescription on mitochondrial DNA deletion, respiratory chain complexes and ATP synthesis in aged rats]

OBJECTIVE

To investigate the effect of Wuzi Yanzong Pill (WZYZP) and its disassembled prescription on mitochondrial DNA deletions, respiratory chain complexes and ATP synthesis in aged rats.

METHODS

Animal experiments with polymerase chain reaction (PCR), enzyme kinetics and bioluminescence technique were conducted.

RESULTS

WZYZP and its disassembled prescription of Fructus Lycii and Semen Cuscutae could reduce the mitochondrial DNA deletions and raise the activities of mitochondrial respiratory chain complexes I, IV and adenosine triphosphate (ATP) synthesis in aged rats' brain; Fructus Lycii and Semen Cuscutae could also reduce the mitochondrial DNA deletions in aged rats' heart (P < 0.05, P < 0.01).

CONCLUSION

WZYZP, Fructus Lycii and Semen Cuscutae have protective effect on oxidative damage of mitochondrial DNA in aged rats.

[Alterations in the level of calcitonin gene related peptide and endothelin-1 in the cirrhotic rat heart]

OBJECTIVE

To investigate the role of calcitonin gene related peptide(CGRP) and endothelin-1 (ET-1) in cirrhotic cardiomyopathy (CCM).

METHODS

We measured the level of CGRP and ET-1 in the samples of rat heart collected from 15 liver cirrhosis rats and 15 controls by using radio immunoassay.

RESULTS

The data showed that the levels of CGRP (74.2130 +/- 10.3776 pg/mg protein) and ET-1 level (1.4780 +/- 0.9235 pg/mg protein) were significantly higher in the cirrhotic rat hearts than those in controls (P < 0.05). The increase of ET-1 in the cirrhotic rat hearts was closely associated with the severity of liver cirrhosis (P = 0.004); whereas no significant association was seen between the CGRP concentration and the severity of liver cirrhosis (P = 0.307).

CONCLUSION

We infer that the increasing of CGRP level in the cirrhotic rat heart may be a protective or antagonistic reaction to ET-1 or other pathogenic factors for cardiac dysfunction. The disturbance of the balance between CGRP and ET-1 in the liver cirrhosis rat hearts may contribute to the pathologic process of CCM.

[TGF beta 1 and ET-1 expression in the peripheral blood of patients with cirrhosis]

OBJECTIVE

The aims of this study were to determine 1. the variation of blood TGF beta 1 and ET-1 in patients with liver cirrhosis; 2. the relationship of the blood TGF beta 1 and ET-1 with Child degree of liver function and the severity of esophageal varices.

METHODS

Peripheral blood samples were obtained from 72 patients and 24 normal controls. The blood levels of TGF beta 1 and ET-1 were measured by using a standard bioassay and the radioimmunoassay.

RESULTS

TGF beta 1 level (11.77 +/- 1.32 ng/ml) and ET-1 level (78.37 +/- 17.54 pg/ml) were significantly higher in the patients than those in controls(P < 0.05). The increase of the ET-1 in the patients is closely associated with Child degree of liver function (r = 0.94) and the severity of esophageal varices(r = 0.87). TGF beta 1 concentration is not associated with Child degree of liver function (r = 0.11) and the severity of esophageal varices (r = 0.03).

CONCLUSION

TGF beta 1 and ET-1 may play an important role in the pathophysiologic process of cirrhosis. ET-1 concentration may reflect portal hypertension development.

Supramolecular origins of product selectivity for methanol-to-olefin catalysis on HSAPO-34

Ethylene selectivity in methanol-to-olefin (MTO) catalysis is related to the number of methyl groups on benzene rings trapped in the nanocages of the preferred catalyst HSAPO-34. By correlating the time evolutions of the catalysts' 13C NMR spectra and the volatile product distribution following abrupt cessation of methanol flow, we discovered that (in the absence of other adsorbates) propene is favored by methylbenzenes with four to six methyl groups but ethylene is predominant from those with two or three methyl groups. We substantially increased ethylene selectivity by operating at lower methanol partial pressures or higher temperatures, either of which reduces the steady-state average methyl substitution. As a step toward a kinetic analysis of the MTO reaction on HSAPO-34, we treated each nanocage with a methylbenzene molecule as a supramolecule capable of unimolecular dissociation into ethylene or propene and a less highly substituted methylbenzene. Addition of a water molecule to a nanocage containing a methylbenzene produces a distinct supramolecule with unique properties. Indeed, co-feeding water with methanol significantly increased the average number of methyl groups per ring at steady state relative to identical conditions without additional water, and also increased ethylene selectivity, apparently through transition state shape selectivity.

[Effects of transforming growth factor beta 1 on the expression of integrin beta 3 and the activity of focal adhesion kinase on human vascular endothelial cell]

OBJECTIVE

To observe the effects of transforming growth factors beta 1 (TGF beta 1) on the expression of integrin beta 3 and the activity of focal adhesion kinase (FAK).

METHODS

This study was performed on cultured human endothelial cells (EC) by using cell-ELISA and immunoprecipitation-tyrosine kinase assay respectively.

RESULTS

Under the stimulus of TGF beta 1, there a dose-dependent increase in the expression of integrin beta 3 chain in the surface of EC. And after the cultured EC were treated with 5 ng/ml or 10 ng/ml TGF beta 1 for 6 or 24 hours, the FAK activity in EC increased significantly as compared with the control group (P < 0.05).

CONCLUSION

The expression of integrin beta 3 and the activity of FAK on EC were regulated by TGF beta 1, and this regulation may be important in cell adherence, angiogenesis, and in the pathophysiology of atherosclerosis.

The integrity of the ball-and-socket joint between V and C domains is essential for complete activity of a humanized antibody

AF2 is a high affinity murine Ab possessing potent neutralizing activity against human IFN-gamma. In carrying out the modifications to humanize this Ab, we discovered that an initial version displayed affinity for IFN-gamma that was slightly less than that of AF2, but exhibited IFN-gamma-neutralizing activity that was severely diminished. Characterization via site-directed mutagenesis revealed that the majority of this loss in IFN-gamma-neutralizing activity was due to altering the V(H) framework residue at position 11. V(H) position 11 is distal to the binding surface of the Ab; however, it, along with residues 110 and 112, have been identified as forming the socket of a molecular ball-and-socket joint between the V and C domains of the Ig Fab, which influences the elbow angle between these domains. To determine whether disrupting the structure of this joint was the basis for reduced IFN-gamma-neutralizing capacity, we altered residue 148 of C(H1), which with residue 149 comprises the corresponding ball portion of the joint. Changing this single C(H1) domain residue diminished the ability of the Ab to neutralize IFN-gamma to a level similar to that observed with the V(H) alteration. Thus, an intact ball-and-socket joint between the V and C domains in AF2 is required for potent neutralization of IFN-gamma. These results suggest the importance of the elbow angle between Ig V and C domains in Ab activity, and support the hypothesis that this joint can be an important functional element of Ab structure.

Rearrangement with formamide extrusion in the electrospray mass spectra of aminoacylbenzylamines

Several aminoacylbenzylamines and their analogs were synthesized and analyzed by electrospray ionization mass spectrometry together with high-resolution and tandem mass spectrometric techniques. Fragment ions ([M + H - CH3NO](+)) were observed and attributed to a transfer of the benzyl group to the N-terminal amino group, leading to elimination of formamide. The proposed mechanism is supported by accurate mass measurements, and by experiments on deuterium labeling and variations of functional groups.

Selective expression of Nkx-2.2 transcription factor in chicken oligodendrocyte progenitors and implications for the embryonic origin of oligodendrocytes

Recent studies have demonstrated that oligodendrocytes originate from the ventral region of the developing spinal cord. However, the precise neuroepithelial origin of oligodendrocytes remains controversial, and the transcriptional control of oligodendrocyte lineage specification is largely unknown. Here we present evidence that oligodendrocytes in the embryonic chicken spinal cord can be generated from neuroepithelial cells that express the Nkx-2.2 homeodomain transcription factor. Nkx-2.2 expression is initially confined to a narrow stripe of neuroepithelium flanking the floor plate. Later, Nkx-2.2+ cells migrate ventrally and dorsolaterally into the surrounding gray and white matter regions where they undergo rapid proliferation. Double labeling experiments revealed that Nkx-2.2+ cells coexpress markers specific for oligodendrocyte progenitors, e.g., PDGFRalpha+, O4, and R-mAb antigens. In the brain, the Nkx-2.2 cells are also highly migratory and can generate oligodendrocytes. The persistent expression of the Nkx-2.2 homeodomain transcription factor in the oligodendrocyte lineage suggests its important role in the control of oligodendrocyte development.

[Influence of multiple coats of bonding agent on the bond strength of amalgam bonding]

OBJECTIVE

To evaluate the effect of multiple coats of bond on the bond strength of amalgam bonding.

METHODS

One or two layers of Scotch-bond multi-purpose plus dental adhesive agent were applied on the dental walls of two groups of teeth respectively prior to amalgam condensation. The third group was set for control which only had amalgam filling. After one week, thermocycling, shear bond strength were tested for all specimens with 1195-Instron testing machine. Data were analyzed by SPSS 8.0. The SEM observation were made in other five modals with one or two layers bonding.

RESULTS

The shear strengths of two or one layer bond and control one were 25.77, 20.69 and 13.05 MPa separately. The difference among them was statistical significant (P < 0.01).

CONCLUSIONS

The microlocking was more obvious in specimens of two bonding layers.

Inward potassium channel in guard cells as a target for polyamine regulation of stomatal movements

A number of studies show that environmental stress conditions such as drought, high salt, and air pollutants increase polyamine levels in plant cells. However, little is understood about the physiological function of elevated polyamine levels. We report here that polyamines regulate the voltage-dependent inward K(+) channel in the plasma membrane of guard cells and modulate stomatal aperture, a plant "sensor" to environmental changes. All natural polyamines, including spermidine, spermine, cadaverine, and putrescine, strongly inhibited opening and induced closure of stomata. Whole-cell patch-clamp analysis showed that intracellular application of polyamines inhibited the inward K(+) current across the plasma membrane of guard cells. Single-channel recording analysis indicated that polyamine regulation of the K(+) channel requires unknown cytoplasmic factors. In an effort to identify the target channel at the molecular level, we found that spermidine inhibited the inward K(+) current carried by KAT1 channel that was functionally expressed in a plant cell model. These findings suggest that polyamines target KAT1-like inward K(+) channels in guard cells and modulate stomatal movements, providing a link between stress conditions, polyamine levels, and stomatal regulation.

Overproduction of D-hydantoinase and carbamoylase in a soluble form in Escherichia coli

The production of D-hydantoinase and carbamoylase from Agrobacterium radiobacter NRRL B11291 using T7 and trc promoters, respectively, was found to cause protein aggregates in Escherichia coli. We initiated a systematic study aimed at overproducting these two proteins in a soluble form. As a result, the protein aggregate from carbamoylase overproduction could be alleviated with the aid of GroEL/GroES. In contrast, the production of a high level of D-hydantoinase in an active form can be achieved at low temperature (25 degrees C) or by the coproduction of DnaJ/DnaK. Overall, with such approaches both recombinant proteins gain more than a four-fold increase in enzyme activity. In addition, by fusion with thioredoxin, D-hydantoinase activity can be increased 25% more than the unfused counterpart in the presence of DnaJ/DnaK. These results indicate the success of our approaches to overproducing D-hydantoinase and carbamoylase in a soluble form in E. coli.

Fatal occupational injuries in a new development area in the People's Republic of China

Fatal occupational injuries in a new development region in Shanghai in east China are described. All occupational deaths in the East Pujiang New Area during the period 1991 through 1997 were abstracted from multiple, overlapping source documents. There were 426 deaths and a crude mortality rate of 9.1 per 100,000 workers. The death rate was highest in 1995 (14.6%), when expansion in the area was most rapid. The construction sector accounted for 55% of the deaths, followed by manufacturing (23%) and transport, storage, and telecommunications (11%). Falls, collisions, struck by/against incidents, and electrocutions accounted for 80% of all deaths. Falls led all other causes of deaths (33%) and were particularly prevalent in the construction industry (46% of all deaths in construction). The development of ongoing, comprehensive injury surveillance systems in the People's Republic of China will be essential to target and evaluate injury prevention activities in the future.

Fatal occupational injuries in the construction industry of a new development area in east China, 1991 to 1997

Two hundred thirty-five work-related deaths occurred in the construction industry in a new economic development area in eastern China between 1991 and 1997. These fatalities represented 55% of all occupational deaths. The average annual mortality rate was 51.5 per 100,000 construction workers. Falls were the leading cause of death (46.4%). Falls, collisions, struck by/against something, electrocutions, and excavation cave-ins were the main fatality antecedents, accounting for nearly 93.6% of all fatalities. The most common antecedents for incidents with multiple fatalities were falls, crane-related events, poisoning, and fire. These categories of antecedents were similar to those encountered in the construction industry in the United States. These data suggest that organizations need to focus on these event types when planning their prevention activities. Moreover, improved surveillance systems including computerized databases with narrative descriptions of injury events, antecedent factors, and person-time at-risk data are needed to target interventions more precisely.

14-3-3 proteins: structure, function, and regulation

The 14-3-3 proteins are a family of conserved regulatory molecules expressed in all eukaryotic cells. A striking feature of the 14-3-3 proteins is their ability to bind a multitude of functionally diverse signaling proteins, including kinases, phosphatases, and transmembrane receptors. This plethora of interacting proteins allows 14-3-3 to play important roles in a wide range of vital regulatory processes, such as mitogenic signal transduction, apoptotic cell death, and cell cycle control. In this review, we examine the structural basis for 14-3-3-ligand interactions, proposed functions of 14-3-3 in various signaling pathways, and emerging views of mechanisms that regulate 14-3-3 actions.

Synthesis and antimalarial activity of sixteen dispiro-1,2,4, 5-tetraoxanes: alkyl-substituted 7,8,15,16-tetraoxadispiro[5.2.5. 2]hexadecanes

Sixteen alkyl-substituted dispiro-1,2,4,5-tetraoxanes (7,8,15, 16-tetraoxadispiro[5.2.5.2]hexadecanes) were synthesized to explore dispiro-1,2,4,5-tetraoxane SAR and to identify tetraoxanes with better oral antimalarial activity than prototype tetraoxane 1 (WR 148999). The tetraoxanes were prepared either by peroxidation of the corresponding cyclohexanone derivatives in H(2)SO(4)/CH(3)CN or by ozonolysis of the corresponding cyclohexanone methyl oximes. Those tetraoxanes with alkyl substituents at the 1 and 10 positions were formed as single stereoisomers, whereas the five tetraoxanes formed without the stereochemical control provided by alkyl groups at the 1 and 10 positions were isolated as mixtures of diastereomers. Three of the sixteen tetraoxanes were inactive (IC(50)'s > 1000 nM), but five (2, 6, 10, 11, 12) had IC(50)'s between 10 and 30 nM against the chloroquine-sensitive D6 and chloroquine-resistant W2 clones of Plasmodium falciparum compared to corresponding IC(50)'s of 55 and 32 nM for 1 and 8.4 and 7.3 nM for artemisinin. We suggest that tetraoxanes 13, 16, and 17 were inactive and tetraoxanes 4 and 7 were weakly active due to steric effects preventing or hindering peroxide bond access to parasite heme. Tetraoxanes 1, 10, 11, and 14, along with artemisinin and arteether as controls, were administered po b.i.d. (128 mg/kg/day) to P. berghei-infected mice on days 3, 4, and 5 post-infection. At this dose, tetraoxanes 10, 11, and 14 cured between 40% and 60% of the infected animals. In comparison, artemisinin and tetraoxane 1 produced no cures, whereas arteether cured 100% of the infected animals. There was no apparent relationship between tetraoxane structure and in vitro neurotoxicity, nor was there any correlation between antimalarial activity and neurotoxicity for these seventeen tetraoxanes.

Agonist-like activity of antibodies to angiotensin II receptor subtype 1 (AT1) from rats immunized with AT1 receptor peptide

In the present study, rats were immunized with angiotensin II receptor subtype 1 (AT1) receptor peptides for 3 months to see if the immunization produced specific anti-AT1 receptor antibodies and if continuous stimulation for 3 months affected blood pressure or induced morphological changes in the organs containing AT1 receptors. Our results showed that there were constant high levels of circulating antibodies throughout the study period in all rats of the immunized group, but not in the control rats, and that there were almost no significant cross-reactions of antisera with AT2 receptor peptide and alpha1 adrenoceptor peptide, except in four rats, which showed low cross-reactions with alpha1 adrenoceptor and AT2 receptor peptides. When an affinity-purified anti-AT1 receptor antibody was used, it specifically displayed the AT1-stimulatory positive chronotropic effect and also localized AT1 receptors. However, in the immunized group, saturation binding of AT1 in homogenates from kidneys showed no difference either in maximal binding sites (Bmax) or in antagonist affinity (Kd). No difference in mRNA of AT1a was found in either kidney or heart, and no morphological changes in the organs were observed, as compared with the control group. Furthermore, immunization did not cause hypertension. In conclusion, the synthetic peptide corresponding to the second extra-cellular loop of the human AT1 receptor was able to produce highly specific and functionally active anti-AT1 receptor antibodies, but unable to induce pathological structural changes or hypertension.

A gene-enriched BAC library for cloning large allele-specific fragments from maize: isolation of a 240-kb contig of the bronze region

A generic bacterial artificial chromosome (BAC) library from a complex plant genome like maize may not be suitable for some types of genomic analysis, for example, for establishing correlations between the genetic and the physical organization of a given chromosome region. Previously, we carried out extensive genetic analysis of the bronze (Bz) region in Zea mays using a W22 inbred line carrying the Bz-McC allele; however, BAC libraries of that line are neither available nor under construction. Here, we report the isolation of large, adjacent BAC clones of this region from a partial BAC library of W22. We developed a BAC vector suitable for cloning NotI fragments and used it to clone size-fractionated genomic DNA that had been cut to completion with the methylation-sensitive, rare-cutting enzyme NotI. This strategy resulted in a very significant enrichment of large genic DNA. From a library of about 20,000 BACs, containing just two-thirds of a maize genome, we isolated 16 BAC clones of the 110-kb distal Bz fragment and 10 BAC clones of the 130-kb proximal Bz fragment. This recovery means that our strategy resulted in a 15- to 24-fold enrichment of specific sequences. The order of the BAC clones in the 240-kb contig, predetermined from an internal NotI site in the Bz-McC allele was confirmed by hybridization with sequences from sites previously mapped proximal and distal to Bz and by sequencing. To show the general utility of our approach and the value of our partial BAC library, we also isolated BAC clones of other sequences, such as tub4 and the complex R-r allele, contained in the same size fraction of DNA. This is the first report of the use of a BAC vector to clone allele-specific large DNA fragments from a plant with a large genome, circumventing the need to construct a complete BAC library.

Modulation of 14-3-3 protein interactions with target polypeptides by physical and metabolic effectors

The proteins commonly referred to as 14-3-3s have recently come to prominence in the study of protein:protein interactions, having been shown to act as allosteric or steric regulators and possibly scaffolds. The binding of 14-3-3 proteins to the regulatory phosphorylation site of nitrate reductase (NR) was studied in real-time by surface plasmon resonance, using primarily an immobilized synthetic phosphopeptide based on spinach NR-Ser543. Both plant and yeast 14-3-3 proteins were shown to bind the immobilized peptide ligand in a Mg2+-stimulated manner. Stimulation resulted from a reduction in KD and an increase in steady-state binding level (Req). As shown previously for plant 14-3-3s, fluorescent probes also indicated that yeast BMH2 interacted directly with cations, which bind and affect surface hydrophobicity. Binding of 14-3-3s to the phosphopeptide ligand occurred in the absence of divalent cations when the pH was reduced below neutral, and the basis for enhanced binding was a reduction in K(D). At pH 7.5 (+Mg2+), AMP inhibited binding of plant 14-3-3s to the NR based peptide ligand. The binding of AMP to 14-3-3s was directly demonstrated by equilibrium dialysis (plant), and from the observation that recombinant plant 14-3-3s have a low, but detectable, AMP phosphatase activity.