Biomedical subjects

Z Gu

Publications and source records attributed to Z Gu.

At least 55 records · Page 3Linked to original sources

PubMed2000

Consensus and comprehensive linkage maps of bovine chromosome 7.

The objective of this project was to integrate the currently available linkage maps for bovine chromosome 7 (BTA7) by combining data sets from eight research groups. A total of 54 unique markers were typed in eight pedigrees. Multilocus linkage analysis with CRI-MAP produced a bovine chromosome 7 consensus framework map of 27 loci ordered with odds greater than 1000:1. Furthermore, we present a bovine chromosome 7 comprehensive map integrating 54 loci. The locus order is in general agreement with the recently published linkage maps except for one discrepancy. The order of loci BM9289, BMS713, and ILSTS001 was reversed in the consensus framework map relative to the published USDA-MARC bovine chromosome 7 linkage map.

Animals↗

PubMed2000

Model for aging in the basal forebrain cholinergic system.

A key component of the cognitive deficits associated with aging is the loss of function of cholinergic neurons in the basal forebrain due to neuronal losses and decreased cholinergic function of spared neurons. A model to mimic one aspect of this phenomenon is to kill cholinergic neurons selectively in the basal forebrain via administration of the immunotoxin IgG-192-saporin. Here we discuss apoptotic regulators, such as nerve growth factor, in age-associated changes present in the cholinergic system and the role of the NF-kappaB signaling system in cellular commitment to apoptosis. We also examine the age-associated decline in intrinsic response mechanisms, which may account for the age-associated reduction in recovery from both acute and chronic insults to the central nervous system.

Aging↗

PubMed2000

Microwave ablation using a spiral antenna design in a porcine thigh muscle preparation: in vivo assessment of temperature profile and lesion geometry.

INTRODUCTION: Theoretical studies have suggested that microwave energy can increase the depth of heating compared with radiofrequency energy. A spiral microwave antenna design may have advantages over previous designs using smaller designs because the resulting power deposition pattern is considerably larger than the catheter diameter. We tested the efficacy of a spiral antenna using microwave energy in a porcine thigh muscle preparation. METHODS AND RESULTS: In five anesthetized pigs, the thigh muscle was exposed and bathed in heparinized bovine blood (36 degrees to 37 degrees C). A helical microwave catheter with a fiberoptic thermometer attached to the distal end was positioned perpendicular to the thigh muscle. The antenna-tissue interface and tissue temperatures at depths of 3.0 and 6.0 mm were measured. A 915-MHz microwave generator delivered energy at one of three power outputs (50, 100, or 150 W) for 60 seconds. Seventy lesions were created: 50 W (n = 23), 100 W (n = 24), and 150 W (n = 23). The mean depths at 50, 100, and 150 W were 4.3 +/- 1.8 mm, 7.2 +/- 1.7 mm, and 9.4 +/- 0.9 mm, respectively. Lesion depth (R = 0.96, P = 0.05), maximum surface dimension (R = 0.99, P = 0.06), and volume (R = 0.99, P = 0.04) were closely correlated to the power applied. CONCLUSION: Power is an important determinant of lesion size using a spiral microwave antenna. A novel, spiral microwave antenna design can create lesions of significant depth that may be applicable for the ablative therapy of ventricular tachycardia.

Animals↗

PubMed2000

ei24, a p53 response gene involved in growth suppression and apoptosis.

DNA damage and/or hyperproliferative signals activate the wild-type p53 tumor suppressor protein, which induces a G(1) cell cycle arrest or apoptosis. Although the mechanism of p53-mediated cell cycle arrest is fairly well defined, the p53-dependent pathway regulating apoptosis is poorly understood. Here we report the functional characterization of murine ei24 (also known as PIG8), a gene directly regulated by p53, whose overexpression negatively controls cell growth and induces apoptotic cell death. Ectopic ei24 expression markedly inhibits cell colony formation, induces the morphological features of apoptosis, and reduces the number of beta-galactosidase-marked cells, which is efficiently blocked by coexpression of Bcl-X(L). The ei24/PIG8 gene is localized on human chromosome 11q23, a region frequently altered in human cancers. These results suggest that ei24 may play an important role in negative cell growth control by functioning as an apoptotic effector of p53 tumor suppressor activities.

Amino Acid Sequence↗

PubMed2000

The p53-inducible gene EI24/PIG8 localizes to human chromosome 11q23 and the proximal region of mouse chromosome 9.

Activation of the p53 tumor suppressor leads to either a cell cycle arrest or to apoptosis and the factors that influence these responses are poorly understood. It is clear, however, that p53 regulates these processes by inducing a series of downstream target genes. One recently identified p53-target gene, EI24 (alias PIG8), induces apoptosis when ectopically expressed. To better understand the biological properties of EI24 and its potential relevance to disease, in particular cancer, we determined the chromosomal location and pattern of gene expression of EI24. EI24 is widely expressed in adult tissues and throughout mouse embryogenesis. The genomic locus of EI24 was mapped to the proximal region of mouse chromosome 9 and human chromosome 11q23-->q24, a region frequently altered in human cancers. These results suggest that EI24 may play an important role in the p53 tumor suppressor pathway.

Animals↗

PubMed2000

Selection of resistance-conferring mutations in HIV-1 by the nucleoside reverse transcriptase inhibitors (+/-)dOTC and (+/-)dOTFC.

The patterns of resistance-conferring mutations that are selected in HIV-1 reverse transcriptase (RT) by the racemates of 2'-dideoxy-3'-oxa-4'-thiocytidine (+/-)dOTC and its fluorinated derivative (+/-)dOTFC were characterized. Genotypic and phenotypic analyses of HIV-1 clinical isolates and HXB2D variants selected with (+/-)dOTC and (+/-)dOTFC were performed in primary cells and in the MT-2 T cell line. HIV-1 variants selected with (+/-)dOTC or (+/-)dOTFC displayed fivefold decreased susceptibility to the respective compounds. A substitution of methionine to valine was identified at position 184 (M184V) in variants selected with (+/-)dOTC. In contrast, a mutation of lysine to arginine at position 65 (K65R) was found in variants selected with (+/-)dOTFC. These patterns of selected mutations differ from those seen with the individual enantiomers. Studies with mutated recombinant HXB2D-M184V and -K65R confirmed that these mutations are important for phenotypic resistance in MT-2 cells. Clinical isolates that display resistance to (-)2'-deoxy-3'-thiacytidine (3TC) also showed cross-resistance to (+/-)dOTC and (+/-)dOTFC. These studies demonstrate that similar genotypes may be selected by the dOTC and dOTFC compounds to those with the structurally related drug 3TC.

Deoxycytidine↗

PubMed2000

[Neuroprotective effect of N-methyl-D-aspartate receptor antagonists in an experimental glaucoma model in the rat].

PURPOSE: To evaluate the neuroprotective effect of memantine and dizocilpine, which are noncompetitive open-channel blockers of the N-methyl-D-aspartate (NMDA) receptor, on glaucomatous optic neuropathy in an experimental glaucoma model in the rat. METHODS: Experimental glaucoma was induced in the right eyes of 30 Wistar albino rats by intracameral injection of India ink followed by laser trabecular photocoagulation 4 days later. The left eye served as a control. Either memantine, dizocilpine, or phosphate-buffered saline (PBS) was injected intraperitoneally just before trabecular photocoagulation. Five days later, 3% fast blue was injected into both superior colliculi. The eyes were enucleated another 3 days later and flat mounts of the retinas were prepared. Labeled ganglion cells were counted in the area 1 mm away from the optic disc. RESULTS: Five days after laser application, no significant intraocular pressure (IOP) change in the right eye was found among the 3 groups. In eyes treated with memantine or dizocilpine, significantly more ganglion cells were labeled. CONCLUSION: Systemically applied memantine and dizocilpine had a neuroprotective effect against experimental glaucomatous optic neuropathy in the rat.

Animals↗

PubMed2000

Study on DNA polymorphism at D1S8 locus in Hebei Han population.

OBJECTIVE: To study the polymorphism at D1S8 locus and to provide basic information for the construction of DNA fingerprint database and the application in forensic medicine. METHODS: Minisatellite variant repeat-polymerase chain reaction (MVR-PCR) and polyacrylamide gradient gel electrophoresis followed by silver staining were used to detect the variant repeat sequences at D1S8 locus of 240 unrelated individuals in Hebei Han population, and digital codes were obtained. RESULTS: Each individual obtained about 30 digital codes, in which none of two unrelated individuals had the same code. The probability of identity of 30 digital codes was 3.55x10(-11). The percentages of three repeat units, a-type, t-type and o-type were 54.77%, 42.54% and 2.69% respectively. The heterozygosity (H) was 0.9837. The excluding probability of paternity(EPP) and polymorphism information content(PIC) were 0.9669 and 0.9833 respectively. CONCLUSION: Because of its high polymorphic nature, D1S8 locus is a valuable marker for forensic identification and paternity testing.

Chromosome Mapping↗

PubMed2000

[Detection of the asymptomatic infection by human papillomavirus in pregnant women and neonates].

OBJECTIVE: To investigate the state of human papillomavirus (HPV) infection in similar average-aged pregnant women of different gestational periods, in the puerperium and neonates. METHODS: Polymerase chain reaction (PCR) assay was employed to detect HPV-6, 11, 16 and 18 DNA in 30 pregnant women in the first trimester, 42 in the second and 31 in the third (who were followed up to their puerperium), and 30 non-pregnant women asking for intrauterine device in our out-patient clinic were taken as controls. Average age in the four groups showed no significant difference (P > 0.05). Samples from cervical, vaginal exfoliated cells, maternal peripheral blood and nasopharyngeal secretion of the newborns were examined respectively. RESULTS: (1) In the first trimester, HPV-DNA was detected in the cervical, vaginal exfoliated cells of 5 cases and in the maternal peripheral blood of 7 cases. (2) In the second trimester, HPV-DNA was detected in the cervical, vaginal exfoliated cells of 12 cases and in the maternal peripheral blood of 11 cases. (3) In the third trimester, HPV-DNA was detected in the cervical, vaginal exfoliated cells of 23 cases and in the maternal peripheral blood of 18 cases. (4) In the puerperium, HPV-DNA was detected in samples of cervical, vaginal exfoliated cells of 8 cases and maternal peripheral blood of 7 cases. (5) In the control group, HPV-DNA was detected in the cervical, vaginal exfoliated cells of 8 cases and in the maternal peripheral blood of 6 cases. (6) Consecutive examinations were carried out in 31 pregnant women from the third trimester, through labor to 6 weeks of postpartum. HPV-DNA was positive in the cervical, vaginal samples of 17, 21 and 8 cases, respectively, according to the perinatal periods, and in the maternal peripheral blood of 14, 13 and 7 cases, respectively. The result through the above gestational stages was fluctuated in the cervical, vaginal samples of 6 cases and in the maternal peripheral blood of 7 cases. (7) Successive examinations in infants at time of birth, 48-72 h and 6 weeks after birth showed positive HPV-DNA in the nasopharyngeal secretion of 13, 6 cases and 1 case with respect to the examining periods. (8) The positive cases were mainly infected by HPV-16, 18. CONCLUSIONS: (1) Infective rate of HPV is statistically significant in the third trimester, but no significant difference exists among the first trimester, the second trimester, the puerperium or the non-pregnancies. (2) Examining consecutively, the HPV positive rate is found to be decreased after delivery, the positive expression of HPV during the gestational periods exhibited fluctuation. (3) Infective rate of HPV in the neonatal nasopharyngeal specimens tends to decrease with time after delivery.

Adult↗

PubMed2000

[Peroxynitrite mediated acute lung injury induced by lipopolysaccharides in rats].

OBJECTIVE: To explore the roles of peroxynitrite (ONOO(-)) in acute lung injury induced by lipopolysaccharides (LPS). METHODS: Nitrotyrosine (NT), a specific marker of in vivo ONOO(-) production, was detected with immunohistochemical technique in rat lung during endotoxin shock (LPS 5 mg/kg iv). Lung coefficient (LC), lung wet/dry weight ratio (W/D), the contents of water and Evans blue (EB) in lungs were measured after intratracheal insufflation of ONOO(-) with different doses. Monastral blue (MB)-labelled blood vessels and pathological changes in lungs were examined under a light microscope. RESULTS: After 2 or 6 hours of LPS intravenous administration, severe lung injury and positive signals of NT occurred with the latter located in the pulmonary macrophages, endothelia, subendothelial and muscular layers of the pulmonary artery. Administration of exogenous ONOO(-) caused dose-dependent increase in LC, W/D, ater and EB contents and in the number of MB-labelled blood vessels in rat lungs, together with significant pathological alterations such as diffuse alveolar collapse, capillary congestion in the septa and focal hemorrhage. CONCLUSION: In the early stage of endotoxin shock, severe lung injury and ONOO(-) production simultaneously exist, and exogenous ONOO(-) could induce significant dysfunction of microvascular endothelial barrier and lung injury, indicating that ONOO(-) generation in vivo may be involved in the pathogenesis of acute lung injury.

Animals↗

PubMed2000

[Effect of chrysotile and cigarette smoking solution on DNA damage and repair in human alveolar epithelial cells].

OBJECTIVE: To study the effect of chrysotile and solution of cigarette smoke separately or combined on DNA damage and repair. METHODS: Single-cells gel electrophoresis assay was used to detect break in DNA strand and to analyze its repair function in human alveolar epithelial cell line A549, which were exposed to chrysotile or cigarette smoke solution separately or combined for one hour and then immediately cultured for different time. RESULTS: Break in DNA strands was induced obviously in A549 cells after exposure to 40 microg/ml of chrysotile or 2.5 x 10(-4) cig/ml of cigarettes smoke solution for one hour. Repair for DNA break could be seen clearly in chrysotile-treated cells after continuing culture for three hours, and 30.6% had been repaired after culture for four hours. Repair could also be seen clearly in cigarette smoke solution-treated cells after continuing culture for two hours, and 65.2% had been repaired after culture for four hours. Repair of DNA in cells exposed to both chrysotile and cigarette smoke solution combined was similar to that exposed to cigarette smoke solution only. CONCLUSION: Damage to DNA caused by chrysotile is more difficult to repair than that induced by cigarette smoking solution.

Asbestos, Serpentine↗

PubMed2000

[Antigen loading on dendritic cells affects the cell function in stimulating T cells].

OBJECTIVE: To study the effect of antigen loading on dendritic cells (DC). METHODS: DCs collected from peripheral blood monocytes were loaded with a tumor antigen from XG-7 cell line. These DCs were then co-cultured with allogeneic T cells and were compared with those DCs without antigen exposure. RESULTS: Although DCs showed no change in their phenotypes after cultured with the antigen, they secreted more IL-12, and became more powerful in allogenic mixed lymphocyte reaction (MLR). Antigen-loaded DC stimulated more CD(4)(+) cells to proliferate than nonantigen-loaded DCs did. These CD(4)(+) cells did not kill XG-7 cells, but promoted CD(8)(+) cells' ability to inhibit the XG-7 proliferation. CONCLUSION: The proliferation of CD(4)(+) cells after cultured with DC may become an indicator for the function of antigen loaded DC and for the efficiency of DC immunotherapy.

Antigens, Neoplasm↗

PubMed2000

[Comparison of the effects of xianyu tablet and its component on electrophoretic mobility of serum LDL and expression of ET-1 mRNA and iNOS mRNA of vessel wall in atherosclerotic rabbits].

Xiaoyu tablet, a compound preparation of Chinese herbal medicines, consists of Radix Salviae Miltiorrhizae(SM) and Fructus Crataegi(FC) extracts. To determine whether the proved recipe was reasonable, the effects of Xiaoyu tablet and its component on electrophoretic mobility of serum LDL and expression of ET-1 mRNA and iNOS mRNA of vessel wall in atherosclerotic rabbits were observed. The results indicated that inhibition of expression iNOS mRNA in vessel wall by Xiaoyu tablet was the same as its single extract of SM or FC, but Xiaoyu talbet was superior to SM or FC extract in reduction of electrophoretic mobility of serum LDL and inhibition of ET-1 mRNA expression in vessel wall. These results suggested that there was obvious synergism on prevention and treatment of atherosclerosis when both of the Chinese herbal medicines were simultaneously used.

Animals↗

PubMed2000

[Examinations of distortion product otoacoustic emission in hereditary progressive non-syndromic hearing loss].

OBJECTIVE: To evaluate the hearing function in patients with hereditary progressive non-syndromic hearing loss. METHODS: Distortion product otoacoustic emissions (DPOAE) and pure tone audiometry were carried out in 52 individuals from a family with non-syndromic hearing loss and 15 persons with normal hearing. RESULTS: 1. Sensorineural hearing loss (SNHL) was found in 34 individuals of the family. Among these individuals, DPOAE was totally absent in 15 cases (29 ears) with pure tone average > or = 40 dB and low amplitude or absent middle to high frequencies in 12 cases (23 ears) with high frequency hearing loss but pure tone average < or = 35 dB. 2. Among 21 individuals (42 ears) with normal audiograms, DPOAE presented lower amplitude or absent high and middle frequencies in 12 individuals. CONCLUSION: DPOAE can be used in identification of subclinical pathologic alterations in the cochlea. This would be of particular value in early diagnosis and genetic consultation.

Audiometry, Pure-Tone↗

PubMed1999

Effects of quercetin on the release of endothelin, prostacyclin and tissue plasminogen activator from human endothelial cells in culture.

Quercetin and related flavonoids are naturally occurring polyphenolic compounds with multiple pharmacological activities. Using cultured human umbilical vein endothelial cells, we investigated the effects of quercetin on endothelin (ET-1) and tissue plasminogen activator (t-PA) release induced by thrombin. We observed that when endothelial cells pretreated with 5 or 50 microM of quercetin were incubated for 4 and 24 h with thrombin, ET-1 concentration-dependently decreased (n = 6, P < 0.01, at 4 h IC50 = 1.54 microM, at 24 h IC50 = 2.78 microM). Under the same experimental conditions, quercetin significantly increased t-PA (n = 6, P < 0.01, at 4 h EC50 = 0.71 microM and at 24 hrs EC50 = 0.74 microM). In the same preparation, we evaluated prostacyclin (PGI2) release, induced by thrombin activated platelets, as determined by a 6-Keto-PGF1alpha radioimmunoassay. Following the treatment of cultured endothelial cells with activated platelets, the concentration of 6-Keto-PGF1alpha was significantly increased (P < 0.01). Quercetin (1, 5, and 20 microM) inhibited PGI2, in a concentration-dependent manner (n = 6, P < 0.05). Our data indicate that quercetin modulates the release of ET-1, t-PA, and PGI2 from vascular endothelial cells.

6-Ketoprostaglandin F1 alpha↗

PubMed1999

Solution structure of the (+)-cis-anti-benzo[a]pyrene-dA ([BP]dA) adduct opposite dT in a DNA duplex.

Minor adducts, derived from the covalent binding of anti-benzo[a]pyrene-7,8-dihydroxy-9,10-epoxide to cellular DNA, may play an important role in generating mutations and initiating cancer. We have applied a combined NMR-computational approach including intensity based refinement to determine the solution structure of the minor (+)-cis-anti-[BP]dA adduct positioned opposite dT in the d(C1-T2-C3-T4-C5-[BP]A6-C7-T8-T9-C10-C11). (d(G12-G13-A14-A15-G16-T17-G18-A19-G20+ ++-A21-G22) 11-mer duplex. The BP ring system is intercalated toward the 5'-side of the [BP]dA6 lesion site without disrupting the flanking Watson-Crick dC5.dG18 and [BP]dA6.dT17 base pairs. This structure of the (+)-cis-anti-[BP]dA.dT 11-mer duplex, containing a bay region benzo[a]pyrenyl [BP]dA adduct, is compared with the corresponding structure of the (+)-trans-anti-[BPh]dA.dT 11-mer duplex (Cosman et al., Biochemistry 32, 12488-12497, 1993), which contains a fjord region benzo[c]phenanthrenyl [BPh]dA adduct with the same R stereochemistry at the linkage site. The carcinogen intercalates toward the 5'-direction of the modified strand in both duplexes (the adduct is embedded within the same sequence context) with the buckling of the Watson-Crick [BP]dA6.dT17 base pair more pronounced in the (+)-cis-anti-[BP]dA.dT 11-mer duplex compared to its Watson-Crick [BPh]dA.dT17 base pair in the (+)-trans-anti-[BPh]dA.dT 11-mer duplex. The available structural studies of covalent polycyclic aromatic hydrocarbon (PAH) carcinogen-DNA adducts point toward the emergence of a general theme where distinct alignments are adopted by PAH adducts covalently linked to the N(6) of adenine when compared to the N(2) of guanine in DNA duplexes. The [BPh]dA and [BP]dA N(6)-adenine adducts intercalate their polycyclic aromatic rings into the helix without disruption of their modified base pairs. This may reflect the potential flexibility associated with the positioning of the covalent tether and the benzylic ring of the carcinogen in the sterically spacious major groove. By contrast, such an intercalation without modified base pair disruption option appears not to be available to [BP]dG N(2)-guanine adducts where the covalent tether and the benzylic ring are positioned in the more sterically crowded minor groove. In the case of [BP]dG adducts, the benzopyrenyl ring is either positioned in the minor groove without base pair disruption, or if intercalated into the helix, requires disruption of the modified base pair and displacement of the bases out of the helix.

Adenine↗

PubMed1999

Solution structure of the N-(deoxyguanosin-8-yl)-1-aminopyrene ([AP]dG) adduct opposite dA in a DNA duplex.

Solution structural studies have been undertaken on the aminopyrene-C(8)-dG ([AP]dG) adduct in the d(C5-[AP]G6-C7). d(G16-A17-G18) sequence context in an 11-mer duplex with dA opposite [AP]dG, using proton-proton distance and intensity restraints derived from NMR data in combination with distance-restrained molecular mechanics and intensity-restrained relaxation matrix refinement calculations. The exchangeable and nonexchangeable protons of the aminopyrene and the nucleic acid were assigned following analysis of two-dimensional NMR data sets on the [AP]dG.dA 11-mer duplex in H2O and D2O solution. The broadening of several resonances within the d(G16-A17-G18) segment positioned opposite the [AP]dG6 lesion site resulted in weaker NOEs, involving these protons in the adduct duplex. Both proton and carbon NMR data are consistent with a syn glycosidic torsion angle for the [AP]dG6 residue in the adduct duplex. The aminopyrene ring of [AP]dG6 is intercalated into the DNA helix between intact Watson-Crick dC5.dG18 and dC7.dG16 base pairs and is in contact with dC5, dC7, dG16, dA17, and dG18 residues that form a hydrophobic pocket around it. The intercalated AP ring of [AP]dG6 stacks over the purine ring of dG16 and, to a lesser extent dG18, while the looped out deoxyguanosine ring of [AP]dG6 stacks over dC5 in the solution structure of the adduct duplex. The dA17 base opposite the adduct site is not looped out of the helix but rather participates in an in-plane platform with adjacent dG18 in some of the refined structures of the adduct duplex. The solution structures are quite different for the [AP]dG.dA 11-mer duplex containing the larger aminopyrene ring (reported in this study) relative to the previously published [AF]dG.dA 11-mer duplex containing the smaller aminofluorene ring (Norman et al., Biochemistry 28, 7462-7476, 1989) in the same sequence context. Both the modified syn guanine and the dA positioned opposite it are stacked into the helix with the aminofluorene chromophore displaced into the minor groove in the latter adduct duplex. By contrast, the aminopyrenyl ring participates in an intercalated base-displaced structure in the present study of the [AP]dG.dA 11-mer duplex and in a previously published study of the [AP]dG.dC 11-mer duplex (Mao et al., Biochemistry 35, 12659-12670, 1996). Such intercalated base-displaced structures without hydrogen bonding between the [AP]dG adduct and dC or mismatched dA residues positioned opposite it, if present at a replication fork, may cause polymerase stalling and formation of a slipped intermediate that could produce frameshift mutations, the most dominant mutagenic consequence of the [AP]dG lesion.

2-Acetylaminofluorene↗

PubMed1999

Solution structures of aminofluorene [AF]-stacked conformers of the syn [AF]-C8-dG adduct positioned opposite dC or dA at a template-primer junction.

A solution structural study has been undertaken on the aminofluorene-C8-dG ([AF]dG) adduct located at a single-strand-double-strand d(A1-A2-C3-[AF]G4-C5-T6-A7-C8-C9-A10-T11-C12-C13). d(G14-G15-A16-T17-G18-G19-T20- A21-G22-N23) 13/10-mer junction (N = C or A) using proton-proton distance restraints derived from NMR data in combination with intensity-based relaxation matrix refinement computations. This single-strand-double-strand junction models one arm of a replication fork composed of a 13-mer template strand which contains the [AF]dG modification site and a 10-mer primer strand which has been elongated up to the modified guanine with either its complementary dC partner or a dA mismatch. The solution structures establish that the duplex segment retains a minimally perturbed B-DNA conformation with Watson-Crick hydrogen-bonding retained up to the dC5.dG22 base pair. The guanine ring of the [AF]dG4 adduct adopts a syn glycosidic torsion angle and is displaced into the major groove when positioned opposite dC or dA residues. This base displacement of the modified guanine is accompanied by stacking of one face of the aminofluorene ring of [AF]dG4 with the dC5.dG22 base pair, while the other face of the aminofluorene ring is stacked with the purine ring of the nonadjacent dA2 residue. By contrast, the dC and dA residues opposite the junctional [AF]dG4 adduct site adopt distinctly different alignments. The dC23 residue positioned opposite the adduct site is looped out into the minor groove by the aminofluorene ring. The syn displaced orientation of the modified dG with stacking of the aminofluorene and the looped out position of the partner dC could be envisioned to cause polymerase stalling associated with subsequent misalignment leading to frameshift mutations in appropriate sequences. The dA23 residue positioned opposite the adduct site is positioned in the major groove with its purine ring aligned face down over the van der Waals surface of the major groove and its amino group directed toward the T6.A21 base pair. The Hoogsteen edge of the modified guanine of [AF]dG4 and the Watson-Crick edge of dA23 positioned opposite it are approximately coplanar and directed toward each other but are separated by twice the hydrogen-bonding distance required for pairing. This structure of [AF]dG opposite dA at a model template-primer junctional site can be compared with a previous structure of [AF]dG opposite dA within a fully paired duplex [Norman, D., Abuaf, P., Hingerty, B. E., Live, D. , Grunberger, D., Broyde, S., and Patel, D. J. (1989) Biochemistry 28, 7462-7476]. The alignment of the Hoogsteen edge of [AF]dG (syn) positioned opposite the Watson-Crick edge of dA (anti) has been observed for both systems with the separation greater in the case of the junctional alignment in the model template-primer system. However, the aminofluorene ring is positioned in the minor groove in the fully paired duplex while it stacks over the junctional base pair in the template-primer system. This suggests that the syn [AF]dG opposite dA junctional alignment can be readily incorporated within a duplex by a translation of this entity toward the minor groove.

Base Pairing↗