Foraging resources of adult Mexican corn rootworm (Coleoptera: Chrysomelidae) in Bell County, Texas

Pollen analyses were used to determine pollen foraging resources of adult Mexican corn rootworms, Diabrotica virgifera zeae Krysan & Smith, captured near Temple, Bell County, TX, in 1996 and 1997. In 1996, adult Mexican corn rootworms were captured in a corn, Zea mays L., field. In 1997, nine locations outside of cornfields were added. Overall, 92% of the beetles (n = 1,323) contained pollen. More than 142,000 pollen grains were counted, representing 45 families, 63 genera, and 27 species. Overall, in 1996, noncorn grass pollen (70%) occurred in the greatest percentage of total pollen followed by corn (17%), then nongrass pollen (13%). In 1997, noncorn grass pollen (76%) had the greatest percentage, then nongrass (18%), and finally corn pollen (6%). Corn pollen was found in 34% of the beetles in 1996 and 26% in 1997. Fifteen Asteraceae taxa were encountered including sunflower, Helianthus annuus L. Thirteen Fabaceae were found including soybean, Glycine max L. Mexican corn rootworm adults foraged mainly on noncorn grass pollen, but also foraged on pollen from a large diversity of plant species, indicating that noncorn pollen may play a role in the food habits of Mexican corn rootworm adults.

Uracil-DNA glycosylase-DNA substrate and product structures: conformational strain promotes catalytic efficiency by coupled stereoelectronic effects

Enzymatic transformations of macromolecular substrates such as DNA repair enzyme/DNA transformations are commonly interpreted primarily by active-site functional-group chemistry that ignores their extensive interfaces. Yet human uracil-DNA glycosylase (UDG), an archetypical enzyme that initiates DNA base-excision repair, efficiently excises the damaged base uracil resulting from cytosine deamination even when active-site functional groups are deleted by mutagenesis. The 1.8-A resolution substrate analogue and 2.0-A resolution cleaved product cocrystal structures of UDG bound to double-stranded DNA suggest enzyme-DNA substrate-binding energy from the macromolecular interface is funneled into catalytic power at the active site. The architecturally stabilized closing of UDG enforces distortions of the uracil and deoxyribose in the flipped-out nucleotide substrate that are relieved by glycosylic bond cleavage in the product complex. This experimentally defined substrate stereochemistry implies the enzyme alters the orientation of three orthogonal electron orbitals to favor electron transpositions for glycosylic bond cleavage. By revealing the coupling of this anomeric effect to a delocalization of the glycosylic bond electrons into the uracil aromatic system, this structurally implicated mechanism resolves apparent paradoxes concerning the transpositions of electrons among orthogonal orbitals and the retention of catalytic efficiency despite mutational removal of active-site functional groups. These UDG/DNA structures and their implied dissociative excision chemistry suggest biology favors a chemistry for base-excision repair initiation that optimizes pathway coordination by product binding to avoid the release of cytotoxic and mutagenic intermediates. Similar excision chemistry may apply to other biological reaction pathways requiring the coordination of complex multistep chemical transformations.

Entry distribution, fission barrier, and formation mechanism of 254102No

The entry distribution in angular momentum and excitation energy for the formation of 254No has been measured after the 208Pb(48Ca,2n) reaction at 215 and 219 MeV. This nucleus is populated up to spin 22Planck's over 2pi and excitation energy greater, similar6 MeV above the yrast line, with the half-maximum points of the energy distributions at approximately 5 MeV for spins between 12Planck's over 2pi and 22Planck's over 2pi. This suggests that the fission barrier is greater, similar5 MeV and that the shell-correction energy persists to high spin.

Detection of DNA alkylphosphotriesters by 32P postlabeling: evidence for the nonrandom manifestation of phosphotriester lesions in vivo

Many genotoxic carcinogens react with the sugar-phosphate backbone in DNA to form phosphotriester (PTE) adducts. These lesions are relatively abundant and persistent for some alkylating carcinogens and may therefore serve as useful biomarkers with which to assess genotoxic exposure and potential mutagenic risk. In the present study, we have developed a 32p postlabeling method that permits analysis of total methyl and/or ethyl PTE in DNA at the femtomole level. The technique is based on the inability of all known nucleolytic enzymes to cleave the internucleotide PTE bond. Consequently, complete digestion of alkylated DNA with these nucleases in the presence of an alkaline phosphatase yields PTE-dinucleoside phosphates. These species are then converted to the corresponding dinucleoside phosphates (dNpdNs) by treatment with alkali to permit subsequent 32p labeling. The resulting labeled dinucleotides (32pd-NpdN) are then analyzed by PAGE. Validation of this method has been carried out using a polydeoxythymidylic acid oligonucleotide containing a site-specific methyl PTE. The method has been applied to the in vitro analysis of calf thymus (CT) DNA treated with dimethylsulfate (DMS) or diethylsulfate (DES) and to the analysis of liver DNA from mice treated in vivo with nitrosodiethylamine. In each case, autoradiograms of the polyacrylamide gels showed the anticipated five bands representing the sixteen labeled dinucleotides, with proportional increases observed as the concentrations of DMS or DES used in the in vitro treatment of CT DNA were increased. The identity and frequency of the nucleosides located 5' to the PTE lesions were obtained by nuclease P1 digestion of the gel-isolated 32pdNpdN species and by analysis of the released labeled mononucleotides, 32pdN, by high-performance liquid chromatography with radioactivity detection. Results obtained from CT DNA treated with DMS or DES showed that the frequency of the four detected nucleotides reflected the normal nucleoside content of CT DNA, indicating the random formation of methyl and ethyl PTE adducts in the in vitro modified DNA. However, studies using liver DNA from three strains of mice treated in vivo with nitrosodiethylamine indicated that the frequency of the thymidine and the 2'-deoxyguanosine 5' to the ethyl PTE was significantly different from the corresponding normal nucleoside content. These results are indicative of (a) the nonrandom formation of ethyl PTE in vivo and/or (b) base sequence-specific ethyl PTE repair.

Guillain-Barré syndrome: delayed diagnosis following anaesthesia

Guillain-Barré syndrome following anaesthesia or surgery is rare. Diagnosis is often delayed, which may lead to an increase in morbidity. There is now good evidence that early diagnosis and treatment reduces this morbidity. The two cases highlight the difficulties with diagnosis in the perioperative period and further discuss the aetiology, diagnostic features and complications of childhood Guillain-Barré syndrome.

SVPD-post-labeling detection of oxidative damage negates the problem of adventitious oxidative effects during 32P-labeling

The exploitation of oxidative DNA lesions as biomarkers of oxidative stress in vivo requires techniques that allow for the precise and valid measurement of oxidative damage to DNA. Previously, endogenous levels of the oxidative lesion 8-hydroxy-2'-deoxyguanosine (8-HO-dG) in rat tissues determined by a micrococcal nuclease/calf spleen phosphodiesterase-based 32P-post-labeling protocol were found to be at least 10-fold higher than those determined by HPLC with electrochemical detection. This was attributed to the adventitious oxidation of the normal nucleotides (dGp) occurring during the labeling stage of the postlabeling protocol, which could only be prevented by the introduction of additional chromatographic steps to remove the unmodified species prior to labeling. In the present study we report that an alternative snake venom phosphodiesterase-based 32P-post-labeling procedure (SVPD-postlabeling) negates the problem of adventitious oxidative damage during labeling by virtue of a unique digestion strategy. In SVPD-post-labeling, digestion yields certain lesions (thymine glycols, phosphoglycolates and abasic sites) as damage-containing dimer species which are ready substrates for labeling. In contrast, the undamaged DNA is recovered as mononucleoside species (dN) which are not substrates for labeling and so remain undetected. Furthermore, even if the mononucleosides are oxidized during labeling, they will not contribute to the level of damage detected. Indeed, we demonstrate that neither the external gamma-irradiation of the digested DNA samples nor increasing the incubation time of the labeling reaction alters the levels of damage detected by SVPD-post-labeling. The negation of adventitious oxidative effects during labeling deems that an optimized SVPD-post-labeling procedure should be well-suited for the biomonitoring of endogenous oxidative stress in vivo.

32P-postlabelling approaches for the detection of 8-oxo-2'-deoxyguanosine-3'-monophosphate in DNA

32P-Postlabelling methods have been investigated for the analysis of the oxidative DNA damage lesion 8-oxoguanine. The extent of digestion of commercially available calf thymus DNA and an 8-oxo-2'-deoxyguanosine-3'-monophosphate (8oxodGp) containing oligonucleotide to 2'-deoxynucleotide-3'-monophosphates, using calf spleen phosphodiesterase and micrococcal nuclease, was determined by HPLC. The extent of unmodified nucleotide release from DNA, and the extent of 8oxodGp released from the oligomer did not increase between 1 and 16 h of incubation at 37 degrees C. Normal nucleotide release from DNA was found to be quantitative under these conditions, and 8oxodGp release from the oligomer was in the range of 84-91%. RNA contamination in DNA prepared for 32P-postlabelling severely compromised 8oxodGp analysis. Guanosine-3'-monophosphate (Gp) was found to exhibit similar chromatographic and electrophoretic properties to 8oxodGp and as such compromised both 8oxodGp isolation in enrichment steps and subsequent resolution of the 32P-labelled bisnucleotides by TLC. The effect of ribonuclease A, T1 and T2 was investigated and a combination of A + T1 was found to reduce Gp contamination in DNA samples to levels which no longer interfered with 8oxodGp analysis. We have successfully applied an HPLC enrichment protocol to the analysis of 8oxodGp in calf thymus DNA. Since determination of damage levels in human samples is often restricted by the amount of DNA available for analysis, a novel capillary electrophoresis (CE) technique for the enrichment of 8oxodGp has been developed. The advantage of CE is that it can achieve resolution of 8oxodGp and unmodified deoxynucleotides from much smaller samples and minimises the amount of [gamma-32P]ATP necessary for the analysis.

DNA containing 4'-thio-2'-deoxycytidine inhibits methylation by HhaI methyltransferase

4'-Thio-2'-deoxycytidine was synthesized as a 5'- protected phosphoramidite compatible with solid phase DNA synthesis. When incorporated as the target cytosine (C*) in the GC*GC recognition sequence for the DNA methyltransferase M. HhaI, methyl transfer was strongly inhibited. In contrast, these same oligonucleotides were normal substrates for the cognate restriction endonuclease R. HhaI and its isoschizomer R. Hin P1I. M. HhaI was able to bind both 4'-thio-modified DNA and unmodified DNA to equivalent extents under equilibrium conditions. However, the presence of 4'-thio-2'-deoxycytidine decreased the half-life of the complex by >10-fold. The crystal structure of a ternary complex of M. HhaI, AdoMet and DNA containing 4'-thio-2'-deoxycytidine was solved at 2.05 A resolution with a crystallographic R-factor of 0.186 and R-free of 0.231. The structure is not grossly different from previously solved ternary complexes containing M. HhaI, DNA and AdoHcy. The difference electron density suggests partial methylation at C5 of the flipped target 4'-thio-2'-deoxycytidine. The inhibitory effect of the 4'sulfur atom on enzymatic activity may be traced to perturbation of a step in the methylation reaction after DNA binding but prior to methyl transfer. This inhibitory effect can be partially overcome after a considerably long time in the crystal environment where the packing prevents complex dissociation and the target is accurately positioned within the active site.

The role of drugs and alcohol in urban minority adolescent suicide attempts

This study examined psychopathology and substance use in 15 African American adolescents who attempted suicide and 15 African American adolescents who did not attempt suicide (control group). Both groups of adolescents and their parents completed questionnaires that addressed depression, behavior problems, family functioning, and drug and alcohol use. On the basis of group means of the Children's Depression Inventory (Kovacs & Beck, 1977), the Youth Self-Report (Achenbach & Edelbrock, 1987), and the Child Behavior Checklist (Achenbach & Edelbrock, 1983), the suicidal youth were found to have a significant level of depression in addition to a variety of internalizing and externalizing behavior disorders. Similarly, on the Multigating Substance Use Evaluation System (Jurkovic & Bruce, 1991), the suicidal youth were at a high risk for alcohol and drug abuse. The suicidal group reported more alcohol and drug abuse than the control group. The results indicated that suicidal African American adolescents used significant amounts of drugs and alcohol, which may be associated with suicide attempts.

The role of endogenous nitric oxide synthesis in contractility of term or preterm human myometrium

OBJECTIVE

To assess in vitro the role of endogenous myometrial nitric oxide synthesis on human myometrial contraction.

DESIGN

Strips of myometrium were mounted in a standard organ bath for assessment of isometric contraction and the response to modulators of nitric oxide synthesis determined.

SETTING

A teaching hospital research laboratory.

SAMPLE

Women undergoing elective nonlabour caesarean section under regional anaesthesia: 54 at term and seven preterm.

RESULTS

Neither addition of L-arginine, the substrate for nitric oxide synthase, nor of an inhibitor of nitric oxide synthase led to any specific change in spontaneous myometrial contraction.

CONCLUSION

Endogenous nitric oxide production does not play an important role in the control of human term of preterm nonlabouring uterine smooth muscle contractility.

Lack of effect of piperonyl butoxide on unscheduled DNA synthesis in precision-cut human liver slices

In this study the effect of piperonyl butoxide (PBO) on unscheduled DNA synthesis in precision-cut human liver slices has been examined. Liver slices prepared from tissue samples from five human donors were cultured in medium containing [3H]thymidine and 0-2.5 mM PBO using a dynamic organ culture system. After 24 h the liver slices were processed for autoradiographic examination of UDS. As positive controls, liver slices were also cultured with three known genotoxic agents, namely 2-acetylaminofluorene (2-AAF), aflatoxin B1 (AFB1) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). UDS was quantified as the net grain count in centrilobular hepatocytes and as the percentage of centrilobular hepatocyte nuclei with > 5 and > 10 net grains. Compared to control liver slice cultures PBO had no effect on UDS. In contrast, treatment with 0.02 and 0.05 mM 2-AAF, 0.002 and 0.02 mM AFB1 and 0.005 and 0.05 mM PhIP produced significant increases in net grain counts of centrilobular hepatocytes. The greatest induction of UDS was observed in liver slices treated with 0.05 mM PhIP. Treatment with 2-AAF, AFB1 and PhIP also produced increases in the number of centrilobular hepatocyte nuclei with > 5 and > 10 net grains. At the concentrations examined neither PBO, 2-AAF nor PhIP had any significant effect on replicative DNA synthesis in 24 h cultured human liver slices. In cultured liver slices treated with 0.02, but not 0.002, mM AFB1 a significant reduction in the rate of replicative DNA synthesis was observed. These results demonstrate that PBO does not induce UDS in cultured human liver slices. However, all three positive control compounds produced marked significant increases in UDS, thus confirming the functional viability of the human liver slice preparations used in this study. In conclusion, these results provide further evidence that PBO is a non-genotoxic agent which does not damage DNA in human liver.

Investigation of some properties of oligodeoxynucleotides containing 4'-thio-2'-deoxynucleotides: duplex hybridization and nuclease sensitivity

The thermal stabilities of the duplexes formed between 4'-thio-modified oligodeoxynucleotides and their DNA and RNA complementary strands were determined and compared with those of the corresponding unmodified oligodeoxynucleotides. A 16mer oligodeoxynucleotide containing 10 contiguous 4'-thiothymidylate modifications formed a less stable duplex with the DNA target (deltaTm/modification -1.0 degrees C) than the corresponding unmodified oligodeoxynucleotide. However, when the same oligodeoxynucleotide was bound to the corresponding RNA target, a small increase in Tm was observed (deltaTm/modification +0.16 degrees C) when compared with the unmodified duplex. A study to identify the specificity of an oligodeoxynucleotide containing a 4'-thiothymidylate modification when forming a duplex with DNA or RNA containing a single mismatch opposite the modification found the resulting Tms to be almost identical to the wild-type duplexes, demonstrating that the 4'-thio-modification in oligodeoxynucleotides has no deleterious effect on specificity. The nuclease stability of 4'-thio-modified oligodeoxynucleotides was examined using snake venom phosphodiesterase (SVPD) and nuclease S1. No significant resistance to degradation by the exonuclease SVPD was observed when compared with the corresponding unmodified oligodeoxynucleotide. However, 4'-thio-modified oligodeoxynucleotides were found to be highly resistant to degradation by the endonuclease S1. It was also demonstrated that 4'-thio-modified oligodeoxynucleotides elicit Escherichia coli RNase H hydrolysis of the RNA target only at high enzyme concentration.