Receptor-specific regulation of B-cell susceptibility to Fas-mediated apoptosis and a novel Fas apoptosis inhibitory molecule

The susceptibility of primary B cells to Fas (APO-1, CD95)-mediated apoptosis is modulated by signals derived from additional surface receptors: CD40 engagement produces upregulation of Fas expression and marked sensitivity to Fas-induced cell death, whereas antigen receptor engagement, or interleukin-4 receptor (IL-4R) engagement, inhibits Fas killing and thereby produces Fas resistance, even in otherwise susceptible, CD40-stimulated targets. Surface immunoglobulin (sIg) and IL-4R utilize distinct signaling pathways to produce Fas resistance that rely on protein kinase C and signal transducer and activator of transcription 6, respectively sIg signaling for inducible Fas resistance requires nuclear factor-kappaB and depends on new macromolecular synthesis. Proximate mediators for Fas resistance include the known anti-apoptotic gene products Bcl-xL and FLIP (but not Btk), and a novel anti-apoptotic gene that encodes Fas apoptosis inhibitory molecule (FAIM). FAIM was identified by differential display and was cloned as two alternatively spliced forms: FAIM-S is broadly expressed, whereas faim-L expression is tissue specific. faim is highly evolutionarily conserved, suggesting an important function throughout phylogeny. Inducible resistance to Fas-mediated apoptosis is speculated to protect antigen-specific B cells during potentially dangerous interactions with FasL-bearing T cells; the elevated sIg-signaling threshold for inducible Fas resistance in autoreactive, tolerant B cells would insure against autoimmunity. However, aberrant acquisition of Fas resistance may allow autoreactive B cells to escape Fas deletion and malignant lymphocytes to thwart antitumor immunity.

Computer based analyses of the 5'-flanking regions of selected genes involved in the nucleotide excision repair complex

We have previously observed that the mRNA of selected genes involved in nucleotide excision repair appear to be coordinately expressed in human tissues from patients with ovarian cancer, testicular cancer, malignant brain tumors, and other malignancies. Such genes include ERCC1, XPA, XPB, XPD, XPF, and XPG. Coordinate mRNA expression appears to be most impressive in non-malignant tissues. We therefore began to explore possible reasons why such coordinate expression should occur. DNA sequences for the above noted genes were obtained from GeneBank. Two different software programs were applied to the DNA sequence, to the area 5' to the start of exon I of each gene. Analyses were performed by computer. The length of the 5' area assessed, was based on previous reports that determined what portion of the genomic sequence comprised the 5' UTR of the promoter of the respective gene. Based on this approach, potential DNA binding sites for no less than three dozen proteins, were identified in the 5'-flanking region of each of the NER genes studied. For each gene, potential binding sites for activator proteins and for repressor proteins were identified. The 5'-flanking regions for each gene noted above, had binding sites in common for 14 proteins with transcription modulatory activity. Eleven of these proteins are known for activator activity; two are reported to have repressor activity, and one has both repressor and activator function. These data suggest a possible molecular basis for the previously observed coordinate mRNA expression of selected NER genes in human tissue specimens.

[Clinical study on Zhuyu Xiaozhong mixture combined with stereotaxic drainage in treating hypertensive cerebral hemorrhage]

OBJECTIVE

To explore the effective method of integrated traditional Chinese and western medicine (TCM-WM) therapy in treating hypertensive cerebral hemorrhage (HCH).

METHODS

Sixty-one HCH patients were randomly divided into two groups: the treated group (group A, 31 cases) and the control group (group B, 30 cases), the former group was treated with stereotaxic drainage and orally taken Zhuyu Xiaozhong mixture (ZYXZM), and the latter group with stereotaxic drainage alone.

RESULTS

The total effective rate of group A was 83.9%, significantly higher than that of group B (60.0%, P < 0.05). In comparing the two groups, the neurological function recovery, the quality of life and the hematoma absorption in group A were significantly better than those of group B (P < 0.05).

CONCLUSION

ZYXZM combined with stereotaxic drainage is effective in treating HCH. It could promote the neurological function recovery and improve the quality of life as well.

[Study on whole blood photoacoustic spectroscopy for PIH (pregnancy-induced hypertension)]

The whole blood of the normal pregnancy and PIH were checked by photoacoustic spectroscopy device. The results shows that there is a characteristic peak in 630-650 nm of the PIH. The characteristic peak may provide an important basis diagnosis of PIH. Basing the result on this, the author makes a further study on the characteristic peak by adding different anticoagulant into blood. The results show that the EDTA is the best one for the characteristic peak analysis.

The role of Sp1 in the differential expression of transforming growth factor-beta receptor type II in human breast adenocarcinoma MCF-7 cells

Progression of MCF-7 cells from early passage (MCF-7E, <200 passage) to late passage (MCF-7L, >500 passage) correlates with a loss of sensitivity to exogenous TGFbeta1. We have previously shown that loss of TGFbeta sensitivity is due to decreased expression of the transforming growth factor receptor type II (TbetaRII) and is associated with increased tumorigenicity in nude mice. Reduced TbetaRII expression in MCF-7L cells is caused by decreased TbetaRII promoter activity in this cell line. Our previous studies using 5' deletion constructs of this promoter revealed that MCF-7L cells were unable to support transcription of the minimal promoter (-47 to +2) to the same levels as the MCF-7E cells. This region of the promoter contains an Sp1 element at position -25 from the major transcription start site. In this study, we investigated the role of Sp1 in TbetaRII transcription. Mutation of the Sp1 site resulted in decreased transcription of TbetaRII in MCF-7E and MCF-7L cells, indicating that this site played a role in transcription of this promoter. Gel shift assays using the proximal Sp1 site from the TbetaRII promoter showed enhanced DNA:protein complex formation with nuclear proteins isolated from MCF-7E cells compared with MCF-7L cells. Supershift analysis identified this binding activity as Sp1. Western blot analysis of Sp1 levels demonstrated that MCF-7E cells contain increased Sp1 protein compared with MCF-7L cells, paralleling the increased binding activity. Differential Sp1 activity was also demonstrated by higher levels of transcription of an Sp1-dependent insulin-like growth factor II promoter construct in MCF-7E cells compared with MCF-7L cells. Co-transfection of an Sp1 expression vector with a TbetaRII promoter construct in MCF-7L cells induced the expression from the promoter-CAT constructs and resulted in an increase of endogenous TbetaRII protein levels. These results demonstrate that the transcriptional repression of TbetaRII in MCF-7L cells is caused, in part, by lower Sp1 levels.

[GC-MS analysis of volatile componments in root of Ficus hitra]

The volatile components in root of Ficus hitra Vahl were analyzed by GC-MS, the results suggested that the main volatile components in root of Ficus hitra Vahl were Hexadecanoic acid, Oleic acid, Linolic acid and Ethyl Acetate; its ether extract contains Isopsoralen and Bergapten. Coumarins should be one of the effective sections in root of Ficus hitra Vahl.

Various AGC repeat numbers in the coding region of the human transcription factor gene E2F-4

The E2F family of transcription factors regulates the expression of genes required for DNA synthesis and cell cycle control. The AGC triplet repeat in the coding region of the E2F-4 gene, a member of the family, has been reported to be mutated in colorectal cancers with a microsatellite instability (MSI) phenotype. We found a wider range variation of the repeat number in DNAs from tumors, the corresponding normal mucosa, and healthy individuals. A total of 5 repeat variants, ranging from 8 to 17 AGC repeats, was detected in 6 (9.7%) of the 62 healthy individuals and 8 (8.9%) of the 90 normal DNAs of the patients. The wild-type 13 repeat was present in all of these individuals. The variation of the AGC repeat number may be a polymorphism. Further, loss of heterozygosity (LOH) at the E2F-4 locus in the tumor tissues of 2 (25%) of the 8 informative cases was detected. The variation may be a useful marker for detection of LOH in primary tumors.

[Observation of the endothelial healing in rabbit corneal alkali wounds by alizarin red S-trypan blue staining method]

PURPOSE

To study the healing of the corneal endothelial cells in rabbit corneal alkali wounds.

METHODS

26 New Zealand white rabbits were used. A alkali wound was created with a round filter paper, 8 mm in diameter, which was soaked in 0.5 N NaOH for 5 seconds and was placed centrally on the cornea for 60 seconds. The rabbits were killed in 20 minutes; 1, 2, 6, 12 h; 1, 2, 3, 5, 7, 10, 14, 30 days after injury. The corneal endothelium was examined in the light microscope using a lizarin red S-trypan blue staining method.

RESULTS

Twenty minutes after the wound, the corneal endothelial cells were destroyed. 72 hours following the wound, the endothelial cells surrounding the burns became larger, irregular and started to migrate onto the denuded descemet's membrane. The endothelial cells covered the burn with the spindle-shaped cells 7 days after wound.

CONCLUSION

The endothelial damage is healed by the division and migration of remaining endothelial cells at the margin of the wound, which has some characters of fibroblast.

A yeast Golgi E-type ATPase with an unusual membrane topology

E-type ATPases are involved in many biological processes such as modulation of neural cell activity, prevention of intravascular thrombosis, and protein glycosylation. In this study, we show that a gene of Saccharomyces cerevisiae, identified by similarity to that of animal ectoapyrase CD39, codes for a new member of the E-type ATPase family (Apy1p). Overexpression of Apy1p in yeast cells causes an increase in intracellular membrane-bound nucleoside di- and triphosphate hydrolase activity. The activity is highest with ADP as substrate and is stimulated similarly by Ca (2+), Mg(2+), and Mn(2+). The results also indicate that Apy1p is an integral membrane protein located predominantly in the Golgi compartment. Sequence analysis reveals that Apy1p contains one large NH(2)-terminal hydrophilic apyrase domain, one COOH-terminal hydrophilic domain, and two hydrophobic stretches in the central region of the polypeptide. Although no signal sequence is found at the NH(2)-terminal portion of the protein and no NH(2)-terminal cleavage of the protein is observed, demonstrated by the detection of NH(2)-terminal tagged Apy1p, the NH(2)-terminal domain of Apylp is on the luminal side of the Golgi apparatus, and the COOH-terminal hydrophilic domain binds to the cytoplasmic face of the Golgi membrane. The second hydrophobic stretch of Apy1p is the transmembrane domain. These results indicate that Apylp is a type III transmembrane protein; however, the size of the Apy1p extracytoplasmic NH(2) terminus is much larger than those of other type III transmembrane proteins, suggesting that a novel translocation mechanism is utilized.

[TLC-identification of radix Rehmanniae and its mixed medicinal materials in Pharmacopoeia]

In 237 kinds of medicinal meterials included 71 kinds of Chinese patent medicines composed in Pharmacopoeia such as Liuweidihuang Pills, character identify constituent of Radix Rehmanniae was found by TLC, and was successed to use to identification of Radix Rehmanniae in 10 kinds of Chinese patent medicines such as Liuweidihuang Pills.

A common polymorphism in exon 40 of the human mannose 6-phosphate/insulin-like growth factor II receptor gene

Mammalian mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) binds insulin-like growth factor II and ligands containing an M6P recognition marker like the latent transforming growth factor-beta. Its genetic alteration has been associated with tumorigenesis of various tumours. We report here a novel polymorphism in exon 40 of the human M6P/IGF2R gene (6206A-->G, Asn2020Ser). The G allele frequency was 0.347 in Japanese. Observed heterozygosity was 0.468. The polymorphism may be useful for studying loss of heterozygosity in primary tumours and gene imprinting.

Differentiation of embryonic stem cells into neurons and retina-like structure in nude mice

PURPOSE

To investigate the intraocular growth and biological characteristics of mice embryonic stem cells in nude mice.

METHODS

Murine embryonic stem cells (D3 cell line) were cultured and maintained in an undifferentiated state in vitro, then transplanted into the anterior chamber of nude mice. Mophological and immunohistochemical examinations were implemented.

RESULTS

Two to three days after transplantation, yellow-white floating granules, sheets and masses were seen inside the anterior chamber and vitreous cavity, and enlarged gradually. 14-20 days later, the mice were executed. Morphological examination showed that there were undifferentiated cells and some round or polygonal differentiated cells in anterior chamber and vitreous cavity. The morphology of these differentiated cells were similar to that of the retina. The cells were highly positive in NSE staining.

CONCLUSION

The transplanted embryonic stem cells could grow in the eyes of nude mice with tendency to differentiate into neurons and retina-like structure.

[Rapid detection of an HPFH deletion by PCR amplification with three primers bridging the breakpoint]

OBJECTIVE

To establish a rapid and reliable PCR method for detecting a deletional hereditary persistence of fetal hemoglobin (HPFH) found in Chinese.

METHODS

Based on some novel DNA sequences across the 3'breakpoint of a HPFH deletion observed in our laboratory, we designed a PCR amplification with three primers bridging the breakpoint. In this system, oligonucleotide primers have been chosen which allow specific identification of both normal and deletional chromosomes under identical condition in either the same or parallel PCR reactions.

RESULTS

The expected two specific amplification bands were produced; one was 565bp in length and stood for the normal alleles,the other,37bp in length represented the mutant alleles of beta-globin gene cluster. This duplex system could directly genotype DNA samples bearing this type of HPFH deletion.

CONCLUSION

This rapid and inexpensive method could be used as a routine method in the molecular screening of carriers and for the prenatal diagnosis of this disease.

cDNA copies of the testis-specific lactate dehydrogenase (LDH-C) mRNA are present in spermatogenic cells in mice, but processed pseudogenes are not derived from mRNAs that are expressed in haploid and late meiotic spermatogenic cells

Retroposons are a class of genes created by reverse transcribing a processed mRNA and inserting the DNA copy into genomic DNA in germ-line cells. The present study concerns the question: Are retroposons created in meiotic and haploid spermatogenic cells? We demonstrate that polymerase chain reaction amplifies cytoplasmic DNAs with the expected intronless-structure of endogenous reverse transcriptase copies of the processed lactate dehydrogenase C mRNA encoding the testis-specific isoform of lactate dehydrogenase. Quantification of cytoplasmic LDH-C mRNA and endogenous cDNA by competitive RT-PCR and PCR, respectively, indicates that the level of LDH-C cDNA is lower by a factor of about 10(7) than the level of LDH-C mRNA in the cytoplasmic nucleic acids extracted from the testes of 14-day-old mice, and that about 1 in 10(5) meiotic cells contains an endogenous cDNA copy of LDH-C mRNA. A review of the literature reveals that a large number of genes including the LDH-C gene, whose expression is restricted to spermatogenic cells, are always single copy. Collectively, these observations suggest that reverse transcriptase cDNA copies of mRNAs are present in meiotic and haploid spermatogenic cells, but these cDNAs are not integrated into genomic DNA.

Non-radioactive hybridization in microwells using enzyme linked immune sorbent assay for detection of RT-PCR-amplified CK19- and CEA-mRNA

PCR enzyme linked immune sorbent assay (ELISA) was developed for detection of RT-PCR-amplified cytokeratin 19 (CK19) mRNA and carcinoembryonic antigen (CEA) mRNA. The non-radioactive hybridization was performed in a streptavidin-coated microwell with digoxigenin-labeled PCR products and with biotin-labeled capture probe. PCR ELISA was proved to be expedient, simple, sensitive and safe for identification of CK19-, CEA-RT-PCR products. These results were proven by sequencing.

[Significance of detecting E-selectin of serum and pleural effusion in differentiating benign and malignant diseases]

OBJECTIVE

To evaluate the significance of detecting E-selectin of serum and pleural effusion in differentiating benign and malignant diseases.

METHOD

E-selectin of serum and pleural effusion in 23 patients with tuberculous pleurisy and 21 patients with lung cancer involving pleura was detected by ELISA method.

RESULT

E-selectin of serum(44 +/- 5 micrograms/L) and pleural effusion (24 +/- 3 micrograms/L) in patients with tuberculous pleurisy was much higher than that of serum (27 +/- 4 micrograms/L) and pleural effusion (11 +/- 3 micrograms/L) in lung cancer patients (P < 0.01). In addition, E-selection of serum in patients with tuberculous pleurisy was also much higher than that of pleural effusion (P < 0.01). And there was no correlation between E-selectin of serum and that of pleural effusion in patients with tuberculous pleurisy (r = 0.16, P > 0.05).

CONCLUSION

E-selectin of serum and pleural effusion in patients with tuberculous pleurisy is produced from different sources. And E-selectin in patients with tuberculous pleurisy is much higher than those with lung cancer. Thence detecting E-selectin of serum and pleural effusion might be helpful for differentiating benign and malignant diseases.

DNA polymerase beta: effects of gapped DNA substrates on dNTP specificity, fidelity, processivity and conformational changes

Pre-steady-state kinetic analysis was used to compare the catalytic properties of DNA polymerase beta (Pol beta) for single-base gap-filling and regular duplex DNA synthesis. The rate of polymerization (kpol) and the apparent equilibrium dissociation constant of dNTP (Kd) were determined with single-nucleotide gapped DNA substrates for all four possible correct base pairs and twelve possible incorrect base pairs, and the results were compared with those obtained previously with non-gapped primer/template duplex DNA substrates. For correct dNTP incorporation, the use of single-nucleotide gapped DNA led to significant decreases in the Kd of dNTP. Although kpol was little affected, the catalytic efficiency kpol/Kd increased significantly owing to the decreases in Kd. In contrast, for incorrect dNTP incorporation, the use of single-nucleotide gapped DNA substrates did not affect the Kd of dNTP appreciably but caused the kpol (and thus kpol/Kd) for incorrect dNTP incorporation to increase. As a consequence the fidelity of Pol beta was not significantly affected by the use of single-nucleotide gapped DNA substrates. In addition we show that under processive polymerization conditions the processivity of Pol beta increases in the gap-filling synthesis owing to a decreased rate of DNA dissociation. Finally, with a single-nucleotide gapped DNA substrate the rate-limiting conformational change step before chemistry was also observed. However, the preceding fast conformational change observed with duplex DNA substrates was not clearly detected. A possible cause is that in the complex with the gapped DNA, the 8 kDa N-terminal domain of Pol beta already exists in a closed conformation. This interpretation was supported by tryptic digestion experiments.

Cytotoxicity of contact lens care solution to human corneal epithelium in vitro

PURPOSE

To investigate the cytotoxicity of soft contact lens multi-purpose care solutions which are now in common use in China.

METHODS

The cell culture method was used. Cytotoxicity was indicated by significant increases in the number of dead cells relative to controls.

RESULTS

Cells were exposed to soft contact lens care solutions for 15 min. They were irregular in shape and variable in size. The intercellular space increased and variable in size. The intercellular space increased and the cells became scrunken. With the time of exposure elongated, damage of cells became more severe.

CONCLUSIONS

Four kinds of soft contact lens multi-purpose care solutions may have harmful effects on the culture of human corneal epithelial cells. Soaked lenses should be rinsed with saline before being placed in the eyes in order to reduce the potential toxicity of contact lens care solutions.

When an ATPase is not an ATPase: at low temperatures the C-terminal domain of the ABC transporter CvaB is a GTPase

The ATP-binding cassette (ABC) transporters belong to a large superfamily of proteins which share a common function and a common nucleotide-binding domain. The CvaB protein from Escherichia coli is a member of the bacterial ABC exporter subfamily and is essential for the export of the peptide antibiotic colicin V. Here we report that, surprisingly, the CvaB carboxyl-terminal nucleotide-binding domain (BCTD) can be preferentially cross-linked to GTP but not to ATP at low temperatures. The cross-linking is Mg2+ and Mn2+ dependent. However, BCTD possesses similar GTPase and ATPase activities at 37 degrees C, with the same kinetic parameters and with similar responses to inhibitors. Moreover, a point mutation (D654H) in CvaB that completely abolishes colicin V secretion severely impairs both GTPase and ATPase activities in the corresponding BCTD, indicating that the two activities are from the same enzyme. Interestingly, hydrolysis activity of ATP is much more cold sensitive than that of GTP: BCTD possesses mainly GTP hydrolysis activity at 10 degrees C, consistent with the cross-linking results. These findings suggest a novel mechanism for an ABC protein-mediated transport with specificity for GTP hydrolysis.

[Effect of keratinocyte growth factor on corneal epithelial wound healing]

OBJECTIVE

To select effective methods for accelerating corneal epithelial wound healing and treating persistent corneal epithelial defect.

METHODS

Exogenous keratinocyte growth factor (KGF, 0.1 ng/ml - 100 ng/ml) was added to cultures of human corneal epithelial cells and DNA synthesis in corneal epithelial cells was measured with [(3)H]-thymidine incorporation and liquid scintillation techniques. The effective concentration of topical application of KGF was calculated and 1 microg/ml KGF was then applied topically to rabbit eyes. Corneal epithelial defect was measured by a digital computer at different times.

RESULTS

KGF at a dosage ranging from 1 ng/ml to 100 ng/ml enhanced cellular proliferation effectively (the rate of cell proliferation 27.66% - 76.73%) and in a dose-dependent manner (r = 0.9233, P < 0.001). Topical application of KGF significantly accelerated corneal wound healing in rabbits (Epithelial healing rate in the KGF-treated group was 1.77 +/- 0.23 mm(2)/h, while in the PBS-treated group it was 1.49 +/- 0.24 mm(2)/h; P < 0.05).

CONCLUSION

The results suggest that exogenous KGF stimulate proliferation of human corneal epithelial cells and accelerate corneal epithelial wound healing in vivo.

[The combined procedure of limbal transplantation (LT) and penetrating keratoplasty (PK) for severe ocular obsolete chemical or thermal burns]

PURPOSE

To improve the prognosis of grafts for obsolete ocular chemical or thermal burns.

METHODS

LT + PK or PK were performed in 28 eyes with severe chemical or thermal burns. The effects of the two groups were compared.

RESULTS

In LT + PK group(12 eyes), during 5 to 28 months of follow-up, the results showed improved visual acuity in 9 eyes (75%), maintained stable epithelial adhesion without recurrent erosion or persistent epithelial defect in 11 eyes (91.67%), graft transparent in 9 eyes (75%). Nine eyes (75%) showed prevented neovascularization and conjunctival tissue from growing into graft. Allograft rejection were identified in 4 eyes (33.33%). In routine PK group (16 eyes), during 3 to 22 months of follow-up, the results showed improved visual acuity in 4 eyes (25%), maintained stable epithelial adhesion without recurrent erosion or PCED in 8 eyes (50%), graft transparent in 4 eyes (25%). Four eyes (25%) showed prevented neovascularization and conjunctival tissue from growing into cornea.

CONCLUSIONS

Combined procedure of LT and PK is an effective treatment for severe ocular chemical or thermal burns. It can reduce persistent corneal epithelial defect and prevent neovascularization and conjunctival epithelial from growing into cornea thus maintaining graft transparent and improving visual acuity.

Interactions of dedicated export membrane proteins of the colicin V secretion system: CvaA, a member of the membrane fusion protein family, interacts with CvaB and TolC

The antibacterial peptide toxin colicin V uses a dedicated signal sequence-independent system for its secretion in Escherichia coli and requires the products of three genes, cvaA, cvaB, and tolC. As a member of the membrane fusion protein family, CvaA is supposed to form a bridge that connects the inner and outer membranes via interaction with CvaB and TolC, respectively. In this study, we investigated the possible interaction of these proteins. When CvaA or CvaB was absent, the corresponding amount of CvaB or CvaA, respectively, was decreased, and the amounts of both proteins were reduced when TolC was depleted. Translational lacZ fusions showed that TolC did not affect the synthesis of either CvaA-beta-galactosidase or CvaB-beta-galactosidase, and CvaA or CvaB did not affect the synthesis of CvaB-beta-galactosidase or CvaA-beta-galactosidase, respectively. However, the stabilities of CvaA and CvaB proteins were affected by the absence of one another and by that of TolC. The instability of CvaA was more severe in TolC-depleted cells than in CvaB-depleted cells. On the other hand, CvaB was less stable in the absence of CvaA than in the absence of TolC. In addition, using a cross-linking reagent, we showed that CvaA directly interacts with both CvaB and TolC proteins. Taken together, these data support the hypothesized structural role of CvaA in connecting CvaB and TolC.

DNA polymerase beta: multiple conformational changes in the mechanism of catalysis

Stopped-flow fluorescence assay was applied to identify conformational changes in the catalytic cycle of DNA polymerase beta (Pol beta), using a synthetic DNA primer/template containing 2-aminopurine (2-AP) at the template position opposite the incoming dNTP. Two phases of fluorescence change were observed in the stopped-flow fluorescence assay of the incorporation of the correct nucleotide dTTP. The rate of the slow phase corresponds to that of product formation. This slow phase was identified as the result of a rate-limiting conformational change step before chemistry because this slow phase was also observed with a dideoxynucleotide at the 3' end of the primer which prevents chemical bond formation. The fast phase was also attributed to a conformational change step since its dependence on [dTTP] is hyperbolic. The rates of the two phases and their dependence on [dTTP] and [Mg2+] suggest that the fast conformational change is induced by the binding of MgdNTP and the slow conformational change is induced by the binding of the catalytic Mg2+ ion. The same biphasic kinetics with different rates were also observed with the thio analog dTTPalphaS and incorrect nucleotides dATP, dGTP, and dCTP. The structural nature for the two conformational changes has been discussed in relation to the available structural information of this enzyme. The results could help to explain how a polymerase controls and achieves its fidelity with a multiple conformational change mechanism.

[A study on the mechanism of damage to DNA in rats by ethylene oxide]

DNA in the liver, kidney, testes, etc. was amplified with semi-random polymerase chain reaction (PCR) in Wistar male rats exposed to ethylene oxide (EtO) for various times and in control rats with hemoglobin gene-specific primer to study the damage effects of EtO on DNA molecule. Results showed that inhalation of 800 mg/m3 of EtO for six to nine weeks could cause damage to DNA in the liver, kidney and testes, etc. to various extent, with the most serious damage to DNA in the testes.

[Culture of human corneal epithelial cells]

PURPOSE

To select culture technique of human epithelial cells for grafts.

METHODS

Epithelial cells of limbus were collected by improved enzymatic disaggregation or explant technique growth curves and to calculate doubling time. DNA synthesis of cells were measured with 3H-thymidine incorporation and liquid scintillation techniques.

RESULTS

Doubling time of cells which were collected by enzymatic disaggregation and by explant technique were 54.15 +/- 4.28 h and 67.88 +/- 1.96 h (P < 0.01). Cellular DNA synthesis of the former was more active (P < 0.01).

CONCLUSIONS

Epithelial cells which were collected by improved enzymatic disaggregation from limbus include stem cells of corneal epithelium. These cells show more active cellulde proliferation and are fitter for use as grafts.