Biomedical subjects

G C Chen

Publications and source records attributed to G C Chen.

At least 19 recordsLinked to original sources

PubMed2006

Novel external sensor array for capsule endoscopy.

Capsule endoscopy (CE) requires placement of an eight-lead sensor array over the abdomen that receives image and localization data transmitted from the capsule. The current process of applying this array to the skin has several disadvantages: firstly, it is time-consuming; secondly, it can be cumbersome for the patient; and thirdly, it is often difficult to place the leads consistently. A new external sensor array system designed to improve this process was tested. It was hypothesized that the new method would be able to receive the transmitted data adequately during CE. The new method and device were tested on an in-patient who had two sets of sensor arrays, batteries, and data recorders placed on her simultaneously. One set was placed in the standard fashion, which served as the control, while the other set was placed using the novel external method. The data provided by the two recorders were compared and the patient's preferences were noted. The quality of the CE images provided by the two methods was identical, but the CE localization tracings were different, presumably due to movement of the gown and leads during the recording period. No signal interference was noted. The patient preferred the external device. A prepositioned external sensor array is capable of transmitting CE data without any loss in image quality, but the localization tracing differs due to movement of the external array. This new method will require testing with a larger sample size in an outpatient setting to allow full assessment of the clinical value of the new approach.

Aged↗

PubMed2006

Leaching potential of heavy metals (Cd, Ni, Pb, Cu and Zn) from acidic sandy soil amended with dolomite phosphate rock (DPR) fertilizers.

There is an increasing concern on heavy metal leaching from the soils amended with sewage sludge. A column study was conducted to examine the extent of leaching of five important heavy metals (Cd, Ni, Pb, Cu and Zn) from an acidic sandy soil amended with different dolomite phosphate rock (DPR) fertilizers (an application rate of 1% fertilizers) developed from DPR and N-Viro (consisting of biosolids and fly ash) at 0%, 10%, 20%, 30%, 40%, 50% and 100% DPR. Ten leaching events were carried out with each event done at an interval of 7 days and with total leaching volume of 1183mm, which is equivalent to the mean annual rainfall of this region during the period of 2001-2003. Leachate was collected after each leaching event and analyzed for heavy metals. The maximum leachate concentrations of Cd, Ni, Pb, Cu and Zn were all below drinking water quality guidance limits set by Florida Department of Environmental Protection and World Health Organization, suggesting that the application of DPR fertilizers may not pose a threat to water quality by leaching. Most of leachate concentrations of Cd, Ni and Pb were below their detection limits and there were no significant differences between the control and the treatments with different DPR fertilizers. By contrast, there were higher leachate concentrations of Cu and Zn (ranging from 0.7 to 37.1mug Cu/l and 5.1 to 205.6mug Zn/l for all treatments) due to their higher contents in both the soil and different DPR fertilizers compared with Cd, Ni and Pb. The leachate concentrations of Cu and Zn for each treatment decreased with increasing leaching events. The differences in leachate concentrations of Cu and Zn between the control and the treatments with different DPR fertilizers containing N-Viro were significant, especially in the first several leaching events and, moreover, they increased with increasing proportion of N-Viro in the DPR fertilizers. There were similar trends in total losses of Cu and Zn after ten leaching events. Greater differences in both leachate concentrations and total losses of Zn between the control and the treatments containing N-Viro were noted. Total losses of Zn for the treatments containing N-Viro were 3.0-5.1 times higher than those for the control compared with 1.4-2.2 times higher for total losses of Cu, suggesting that greater proportions of Zn losses came from the DPR fertilizers due to the greater mobility of Zn in the DPR fertilizers compared with Cu.

Fertilizers↗

PubMed2005

Use of dolomite phosphate rock (DPR) fertilizers to reduce phosphorus leaching from sandy soil.

There is increasing concern over P leaching from sandy soils applied with water-soluble P fertilizers. Laboratory column leaching experiments were conducted to evaluate P leaching from a typical acidic sandy soil in Florida amended with DPR fertilizers developed from dolomite phosphate rock (DPR) and N-Viro soil. Ten leaching events were carried out at an interval of 7 days, with a total leaching volume of 1,183 mm equivalent to the mean annual rainfall of this region during the period of 2001-2003. Leachates were collected and analyzed for total P and inorganic P. Phosphorus in the leachate was dominantly reactive, accounting for 67.7-99.9% of total P leached. Phosphorus leaching loss mainly occurred in the first three leaching events, accounting for 62.0-98.8% of the total P leached over the whole period. The percentage of P leached (in the total P added) from the soil amended with water-soluble P fertilizer was higher than those receiving the DPR fertilizers. The former was up to 96.6%, whereas the latter ranged from 0.3% to 3.8%. These results indicate that the use of N-Viro-based DPR fertilizers can reduce P leaching from sandy soils.

Calcium Carbonate↗

PubMed2004

Assessment of genetic, antigenic and pathotypic criteria for the characterization of IBDV strains.

The aim of this work was the selection and comparison of representative infectious bursal disease virus (IBDV) strains. Nine strains of IBDV, isolated at different times and from different geographic regions of Europe and China, were characterized. Batches of all strains were prepared following standardized protocols and checked for the absence of contaminating viruses. Criteria used for their characterization were: (i) the nucleotide sequence of the VP2 variable region, (ii) binding to a panel of neutralizing monoclonal antibodies in antigen capture enzyme-linked immunosorbent assays, and (iii) virulence in specific pathogen free chickens after infection with a standardized number of median embryo infective doses. Based on the first two criteria, two of nine strains were classified as classical virulent (cv) IBDV (F52/70, Cu-1wt), and five as very virulent (vv) IBDV (849VB, 96108, HK46, GX, Harbin). Remarkably, although a clear-cut difference was demonstrable between European cvIBDV (F52/70 and Cu-1wt) and vvIBDV (849VB and 96108) strains, there was a continuum in the pathogenicity of Chinese vvIBDVs. Our results indicate the probable existence of differences in virulence within IBDV lineages determined on the basis of antigenic typing using monoclonal antibodies and the alignment of the VP2 sequences. This indicates limitations in the analysis of IBDV pathotypes based on the VP2 variable region and emphasizes that these criteria may not be sufficient for the classification of IBDV strains.

Amino Acid Sequence↗

PubMed2004

Adsorption-desorption characteristics of lead in variable charge soils.

Adsorption desorption processes of Pb at contaminated levels in two variable charge soils were investigated. The red soil (RAR) developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) adsorbed more Pb2+ than the red soil (REQ) derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult). The maximum adsorption values (Xm) that were obtained from the simple Langmuir model were 52.6 mmol Pb2+ kg(-1) soil and 29.9 mmol Pb2+ kg(-1) soil, respectively, for the RAR and REQ. Adsorption of Pb2+ decreased soil pH by 1.10 unit for the RAR soil and 1.21 unit for the REQ soil at the highest loading. The adsorption equilibrium pH of RAR was higher than that of REQ at the same Pb2+ concentration. The distribution coefficient (Kd) of Pb in the soils decreased exponentially with increasing Pb2+ loading. Most of the adsorbed Pb2+ in the soils was not desorbed in the 0.01 mol L(-1) NaNO3 solution. After five successive extractions with NaNO3, only 0-11% of the total adsorbed Pb2+ in the RAR soil was desorbed and the corresponding value of the REQ soil was 0-19%, indicating that the RAR soil had a greater affinity for Pb2+ than the REQ soil at the same Pb2+ loading. Different mechanisms might be involved in Pb2+ adsorption/desorption at different levels of Pb2+ loading and between the two soils.

Adsorption↗

PubMed2001

A protein interaction map for cell polarity development.

Many genes required for cell polarity development in budding yeast have been identified and arranged into a functional hierarchy. Core elements of the hierarchy are widely conserved, underlying cell polarity development in diverse eukaryotes. To enumerate more fully the protein-protein interactions that mediate cell polarity development, and to uncover novel mechanisms that coordinate the numerous events involved, we carried out a large-scale two-hybrid experiment. 68 Gal4 DNA binding domain fusions of yeast proteins associated with the actin cytoskeleton, septins, the secretory apparatus, and Rho-type GTPases were used to screen an array of yeast transformants that express approximately 90% of the predicted Saccharomyces cerevisiae open reading frames as Gal4 activation domain fusions. 191 protein-protein interactions were detected, of which 128 had not been described previously. 44 interactions implicated 20 previously uncharacterized proteins in cell polarity development. Further insights into possible roles of 13 of these proteins were revealed by their multiple two-hybrid interactions and by subcellular localization. Included in the interaction network were associations of Cdc42 and Rho1 pathways with proteins involved in exocytosis, septin organization, actin assembly, microtubule organization, autophagy, cytokinesis, and cell wall synthesis. Other interactions suggested direct connections between Rho1- and Cdc42-regulated pathways; the secretory apparatus and regulators of polarity establishment; actin assembly and the morphogenesis checkpoint; and the exocytic and endocytic machinery. In total, a network of interactions that provide an integrated response of signaling proteins, the cytoskeleton, and organelles to the spatial cues that direct polarity development was revealed.

Actins↗

PubMed2001

Rb-associated protein 46 (RbAp46) inhibits transcriptional transactivation mediated by BRCA1.

The retinoblastoma suppressor (Rb)-associated protein 46 (RbAp46) is a member of the WD-repeat protein family and a component of the histone modifying and remodeling complexes. Previously, we demonstrated that RbAp46 is a potent growth inhibitor that can suppress the transformed phenotype of tumor cells. To explore the molecular mechanisms of RbAp46 function, we used RbAp46 as a bait in a yeast two-hybrid screening and found that RbAp46 interacts specifically with the C-terminal region of BRCA1 (the BRCT domain), a domain involved in the t transactivation activity of BRCA1. Coimmunoprecipitation assays demonstrated that the interaction of RbAp46 with BRCA1 requires the first two of the four Trp-Asp (WD)-repeats of RbAp46. We also showed that expression of RbAp46 represses the transactivation activity mediated by the BRCT/Gal4 fusion protein and inhibits the transactivation of the p21 promoter mediated by the full-length BRCA1. Interestingly, the association of BRCA1 and RbAp46 is disrupted in cells treated with DNA-damaging agents. These results suggest that RbAp46 may specifically interact with BRCA1 and modulate its transactivation activity in response to DNA damage.

BRCA1 Protein↗

PubMed2000

Identification of novel, evolutionarily conserved Cdc42p-interacting proteins and of redundant pathways linking Cdc24p and Cdc42p to actin polarization in yeast.

In the yeast Saccharomyces cerevisiae, Cdc24p functions at least in part as a guanine-nucleotide-exchange factor for the Rho-family GTPase Cdc42p. A genetic screen designed to identify possible additional targets of Cdc24p instead identified two previously known genes, MSB1 and CLA4, and one novel gene, designated MSB3, all of which appear to function in the Cdc24p-Cdc42p pathway. Nonetheless, genetic evidence suggests that Cdc24p may have a function that is distinct from its Cdc42p guanine-nucleotide-exchange factor activity; in particular, overexpression of CDC42 in combination with MSB1 or a truncated CLA4 in cells depleted for Cdc24p allowed polarization of the actin cytoskeleton and polarized cell growth, but not successful cell proliferation. MSB3 has a close homologue (designated MSB4) and two more distant homologues (MDR1 and YPL249C) in S. cerevisiae and also has homologues in Schizosaccharomyces pombe, Drosophila (pollux), and humans (the oncogene tre17). Deletion of either MSB3 or MSB4 alone did not produce any obvious phenotype, and the msb3 msb4 double mutant was viable. However, the double mutant grew slowly and had a partial disorganization of the actin cytoskeleton, but not of the septins, in a fraction of cells that were larger and rounder than normal. Like Cdc42p, both Msb3p and Msb4p localized to the presumptive bud site, the bud tip, and the mother-bud neck, and this localization was Cdc42p dependent. Taken together, the data suggest that Msb3p and Msb4p may function redundantly downstream of Cdc42p, specifically in a pathway leading to actin organization. From previous work, the BNI1, GIC1, and GIC2 gene products also appear to be involved in linking Cdc42p to the actin cytoskeleton. Synthetic lethality and multicopy suppression analyses among these genes, MSB, and MSB4, suggest that the linkage is accomplished by two parallel pathways, one involving Msb3p, Msb4p, and Bni1p, and the other involving Gic1p and Gic2p. The former pathway appears to be more important in diploids and at low temperatures, whereas the latter pathway appears to be more important in haploids and at high temperatures.

Actins↗

PubMed2000

Risk factors for presentation with bleeding in patients with Helicobacter pylori-related peptic ulcer diseases.

At present, there is no study that simultaneously addresses the apparent differences between bacterial and host factors in patients with bleeding and nonbleeding Helicobacter pylori-related ulcer diseases. Therefore, we designed this prospective study to evaluate whether there are identifiable differences between the two groups of patients whose H. pylori-related peptic ulcer diseases present with bleeding or dyspepsia. From July 1996 to November 1996, consecutive patients presenting with upper gastrointestinal bleeding or dyspepsia were enrolled if H. pylori-related ulcer diseases were confirmed. Fifteen clinical, endoscopic, histologic, and serologic factors were tested for association with ulcer bleeding by a logistic regression analysis. In the study period, bleeding occurred in 39 out of 119 patients with H. pylori-related peptic ulcer diseases. Multivariate analysis showed that ingestion of nonsteroidal antiinflammatory drugs (NSAIDs; p = 0.0156; odds ratio = 5:4), ulcer size > or = 1 cm (p = 0.0033; odds ratio = 4:2), and low bacterial density (p = 0.0030; odds ratio = 4:1) were independent factors associated with the risk of bleeding. There were no associations between ulcer bleeding and age, sex, smoking, alcohol consumption, the histologic grade of gastritis, location and number of ulcers, and the cytotoxin-associated gene (CagA) status of H. pylori strain. Therefore, we concluded that H. pylori-related ulcer patients who use NSAIDs or have large ulcers are more likely to present with upper gastrointestinal bleeding; that the CagA-bearing strains are not associated with the development of bleeding complication in patients with peptic ulcer diseases; and that the exact reason concerning the association between low bacterial density and ulcer bleeding merits further investigation.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1998

Antimicrobial effects of metal ions (Ag+, Cu2+, Zn2+) in hydroxyapatite.

The antimicrobial ceramics (AC) based on hydroxyapatite (HA) were made in a wet chemical process with additions of AgNO3, Cu(NO3)2. 3H2O and Zn(NO3)2. 6H2O. The ACs were composed of metal-ion substituted hydroxyapatite and nitrate-apatite, which was identified by X-ray diffraction. The viable count and turbidity measurement was adopted to observe the antimicrobial effects of the various ACs. The aerobic Escherichia coli was used in the study. An obvious antimicrobial effect against E. coli was observed in Ag+ AC. In contrast to Ag+ AC, it was difficult to ascertain any bactericidal effect in the case of Cu2+ and Zn2+ AC. The bactericidal effect of Ag+ was observed using a dialysis tube experiment. This suggests that Ag+ dissolved out and reacted with E. coli, thus inhibiting its growth.

Journal Article↗

PubMed1998

Using the yeast two-hybrid system to identify human epithelial cell proteins that bind gonococcal Opa proteins: intracellular gonococci bind pyruvate kinase via their Opa proteins and require host pyruvate for growth.

Neisseria gonorrhoeae opacity-associated (Opa) proteins are a family of outer membrane proteins involved in gonococcal adherence to and invasion of human cells. We wanted to identify additional roles for Opa in the infectious process and used the yeast two-hybrid system to identify human epithelial cell proteins that interact with Opa proteins. Although this system has been used successfully to identify many types of interacting proteins, it has not been used to screen a human cell cDNA library for binding partners of a prokaryotic outer membrane protein. Therefore, we were also interested in exploring the versatility of the yeast two-hybrid system in identifying bacteria-host interactions. Using OpaP from strain F62SF as bait, we screened a HeLa cell cDNA library for Opa-interacting proteins (OIPs). We identified five different OIPs, designated OIP1-OIP5, two of which are homologous to human proteins--thyroid hormone receptor interacting protein (TRIP6) and pyruvate kinase isoenzyme M2 (PK). In the studies presented here, we investigated the interaction between Opa proteins and PK in more depth. Opa-PK interactions were confirmed by in vitro and in vivo assays independent of the yeast two-hybrid system. Escherichia coli expressing six different Opa proteins from gonococcal strain FA1090 all bound more PK than Opa-negative E. coli in in vitro binding assays. Using anti-PK antibody and fluorescence microscopy, we showed that human epithelial cell PK co-localizes with intracellular Opa+ gonococci and E. coli expressing Opa proteins. Using a mutant of N. gonorrhoeae unable to grow on pyruvate or lactate, it appears that intracellular pyruvate is essential for gonococcal growth and survival. These results suggest a novel mechanism in bacterial pathogenesis, i.e. the requirement for direct molecular interaction with a host metabolic enzyme (PK) for the acquisition of an essential intracellular carbon source and growth substrate (pyruvate). These results demonstrate that the yeast two-hybrid system is a valuable tool for identifying biologically relevant interactions between bacteria and host proteins, providing valuable leads for further investigations into novel mechanisms of bacterial pathogenesis.

Amino Acid Sequence↗

PubMed1998

Geographic variation in viral load among hepatitis B carriers with differing risks of hepatocellular carcinoma.

The risk of hepatocellular carcinoma (HCC) varies significantly among hepatitis B virus (HBV) carriers from different geographic regions. We compared serological markers of HBV infection in adult male carriers from Haimen City, China and Senegal, West Africa, where the prevalence of chronic infection is similar. HCC mortality among HBV carriers is much higher in Haimen City than it is in Senegal (age-standardized rate, 878 versus 68 per l0(5) person-years). A dramatic difference was observed when HBV DNA levels in serum were assessed among carriers by Southern blot. In the Senegalese group (n = 289), 14.5% were HBV DNA positive by Southern blot in their 20s, and this percentage declined in each subsequent decade of age to 3.3, 2.9, and 0% thereafter. In the Chinese group (n = 285), a higher prevalence of HBV DNA positivity and a less consistent reduction were seen; 29.4% were positive in their 20s, and 30.2, 23.6, and 20.6%, respectively, were positive in each subsequent decade of age. Among 102 male Asian-American HBV carriers, the prevalence of HBV DNA positivity was intermediate between the Chinese and Senegalese populations (36.8, 10.7, 3.0, and 4.6% in each subsequent decade of age). Viral titers were similar among those who were HBV DNA positive in all three populations [median value, 10(7) virions/ml (range, 10(6)-10(9) virions/ml)]. The presence of HBV DNA in serum was positively associated with serum glutathione S-transferase, a marker of liver damage. These findings suggest that the more prolonged maintenance of productive virus infection in the Chinese carriers compared with the Senegalese carriers may explain their higher risk of HCC. This profound difference in the natural history of chronic infection may be due to earlier age of infection in China or to as yet unknown environmental or genetic factors.

Adult↗

PubMed1997

The Cdc42 GTPase-associated proteins Gic1 and Gic2 are required for polarized cell growth in Saccharomyces cerevisiae.

BEM2 of Saccharomyces cerevisiae encodes a Rho-type GTPase-activating protein that is required for proper bud site selection at 26 degrees C and for bud emergence at elevated temperatures. We show here that the temperature-sensitive growth phenotype of bem2 mutant cells can be suppressed by increased dosage of the GIC1 gene. The Gic1 protein, together with its structural homolog Gic2, are required for cell size and shape control, bud site selection, bud emergence, actin cytoskeletal organization, mitotic spindle orientation/positioning, and mating projection formation in response to mating pheromone. Each protein contains a CRIB (Cdc42/Rac-interactive binding) motif and each interacts in the two-hybrid assay with the GTP-bound form of the Rho-type Cdc42 GTPase, a key regulator of polarized growth in yeast. The CRIB motif of Gic1 and the effector domain of Cdc42 are required for this association. Genetic experiments indicate that Gic1 and Gic2 play positive roles in the Cdc42 signal transduction pathway, probably as effectors of Cdc42. Subcellular localization studies with a functional green fluorescent protein-Gic1 fusion protein indicate that this protein is concentrated at the incipient bud site of unbudded cells, at the bud tip and mother-bud neck of budded cells, and at cortical sites on large-budded cells that may delimit future bud sites in the two progeny cells. The ability of Gic1 to associate with Cdc42 is important for its function but is apparently not essential for its subcellular localization.

Adaptor Proteins, Signal Transducing↗

PubMed1997

Cryo-electron microscopy of low density lipoprotein and reconstituted discoidal high density lipoprotein: imaging of the apolipoprotein moiety.

Cryo-electron microscopy was used to analyze the structure of low density lipoprotein from normolipidemic subjects (N-LDL), phospholipid-depleted N-LDL (PD-LDL), small dense LDL from hypertriglyceridemic subjects (SD-LDL), and reconstituted discoidal high density lipoproteins (rHDL). In different projections of N-LDL, a high density component of the particle was visible as two parallel bands or as a single ring. Projections of PD-LDL were very similar to those of N-LDL, indicating that the contribution of phospholipid headgroups to the observed high density structure is minor. In preparations of SD-LDL, projections with two high density bands or a single high density ring were rare. Instead, triangular and diamond-shaped projections were recognized. In different projections of discoidal rHDL, a high density component was visible as a single band or as a single ring. The present results indicate that cryo-electron microscopy reveals the distribution of apolipoproteins within lipoprotein particles. Thus, apolipoprotein B-100 (apoB) in N-LDL appears to be organized as a double ring around the particle, while apoB in SD-LDL is indicated to have a different conformation. Cryo-electron micrographs of rHDL are consistent with the presence of apolipoprotein A-I on the periphery of the lipoprotein disc.

Apolipoprotein A-I↗

PubMed1996

Rho1p, a yeast protein at the interface between cell polarization and morphogenesis.

The enzyme that catalyzes the synthesis of the major structural component of the yeast cell wall, beta(1-->3)-D-glucan synthase (also known as 1,3-beta-glucan synthase), requires a guanosine triphosphate (GTP) binding protein for activity. The GTP binding protein was identified as Rho1p. The rho1 mutants were defective in GTP stimulation of glucan synthase, and the defect was corrected by addition of purified or recombinant Rho1p. A protein missing in purified preparations from a rho1 strain was identified as Rho1p. Rho1p also regulates protein kinase C, which controls a mitogen-activated protein kinase cascade. Experiments with a dominant positive PKC1 gene showed that the two effects of Rho1p are independent of each other. The colocalization of Rho1p with actin patches at the site of bud emergence and the role of Rho1p in cell wall synthesis emphasize the importance of Rho1p in polarized growth and morphogenesis.

Cell Polarity↗

PubMed1996

Detection and identification of microcystins in the drinking water of Haimen City, China.

Cyanobacterial toxins, microcystins, have a potent tumor-promoting activity. We investigated the level of microcystins in drinking water collected from 1992 to 1994 in Haimen City, China, where people who drink pond ditch water usually incurred a high incidence rate of hepatocellular carcinoma compared with those who drink well water. High-performance liquid chromatography, liquid chromatography/mass spectrometry (LC/MS), and protein phosphatase inhibition assay (pp assay) were used to identify and quantify the microcystins. Microcystin LR and [D-Asp3]microcystin LR were detected in 2 of 50 samples at a concentration less than 100 ng/L by LC/MS in 1992. Although no microcystins were found by the chemical method in 1993, 6 of 7 samples except for 3 tap water samples showed an approximate amount of 100 ng/L by using the pp assay in 1994. The obtained results supported the epidemiological results reported by Yu.

Bacterial Toxins↗

PubMed1996

Intracellular location of the Saccharomyces cerevisiae CDC6 gene product.

The CDC6 gene product from Saccharomyces cerevisiae is required for transition from late G1 to S phase of the cell cycle. We have investigated the subcellular localization of the CDC6 protein in yeast to explore where Cdc6p exerts its gene function (s). Using affinity-purified sera we localized Cdc6p to the cytoplasm and the nuclear matrix by both subcellular fractionation and indirect immunofluorescence microscopy. The nuclear localization was confirmed to be in the nuclear scaffold by the low-salt extraction method. The Cdc6p cannot be detected in the mitochondrial or plasma membrane fractions. Using indirect immunofluorescence, we found that a subpopulation of Cdc6p migrated into the nucleus after G1/S transition and diminished after M phase, suggesting its temporal role in nuclear DNA replication. The predicted Cdc6p polypeptide contains a conserved nuclear localization, 27PLKRKKL33, similar to that of the SV40 large T antigen and other nuclear proteins. To test whether this peptide segment plays a role in mediating nuclear transport, we have carried out site-directed mutagenesis to alter the conserved 29Lys to Thr and Arg. The wild-type nuclear localization signal of Cdc6p was found to mediate the LacZ reporter gene fused to CDC6 efficiently to the nucleus, but not the mutated versions of the nuclear localization motif. The results suggested that 29Lys is important in mediating nuclear localization, the 29Thr and 29Arg mutant versions of the CDC6 gene were also unable to complement the cdc6 temperature-sensitive mutant. However, when these mutants were expressed from a multicopy plasmid, the mutated genes could complement the mutation. Similar results were obtained in the cdc6-disrupted cells. Taken together, we suggest that (i) Cdc6p is predominantly located in the cytoplasm, (ii) the nuclear entry of Cdc6p is cell cycle dependent, and (iii) nuclear entry of Cdc6p is mediated by its nuclear localization signal. The presence of Cdc6p in both the nucleus and the cytoplasm suggests a model that Cdc6p exerts its gene function in DNA replication and mitotic restraint in the cell cycle.

Amino Acid Sequence↗

PubMed1996

Detection of microcystins, a blue-green algal hepatotoxin, in drinking water sampled in Haimen and Fusui, endemic areas of primary liver cancer in China, by highly sensitive immunoassay.

An epidemiological survey for the causes of a high incidence of primary liver cancer (PLC) in Haimen city, Jian-Su province and Fusui county, Guangxi province in China, found a close correlation between the incidence of PLC and the drinking of pond and ditch water. With an aim to clarify whether microcystins (MC), a hepatotoxic peptide produced by water bloom algae, contaminate the drinking water in the endemic areas of PLC in China, a highly sensitive enzyme-linked immunosorbent assay with a detection limit of 50 pg/ml, was introduced to monitor the MC. Three trials to survey the drinking water were carried out in 1993-1994. Samples, 1135 in total, were collected from different sources such as: ponds, ditches, rivers, shallow wells and deep wells in Haimen city. The first survey in September 1993 found that three out of 14 ditch water specimens were positive for MC, with a range of 90-460 pg/ml. Several toxic algae such as Oscillatoria agardhii were present in some of the ditches. In the second trial, samples were collected from five ponds/ditches, two rivers, two shallow wells and two deep wells monthly for the whole year of 1994. These data showed that MC was highest in June to September, with a range of 62-296 pg/ml. A third trial on the 989 different water samples collected from the different types of water sources in July 1994 revealed that 17% of the pond/ditch water, 32% of the river water, and 4% of the shallow-well water were positive for MC, with averages of 101, 160 and 68 pg/ml respectively. No MC was detected in deep well water. A similar survey on 26 drinking water samples in Fusui, Guangxi province, demonstrated a high contamination frequency of MC in the water of ponds/ditches and rivers but no MC in shallow and deep wells. These data support a hypothesis that the blue-green algal toxin MC in the drinking water of ponds/ditches and rivers, or both, is one of the risk factors for the high incidence of PLC in China. Based on previous findings on the epidemiology of PLC and the present results from the mass screening of MC in the drinking water, an advisory level of MC in drinking water was proposed to below 0.01 microg/l. The combined effect of a potent hepatocarcinogen AFB1 and an intermittent intake of MC in drinking water in the summer season was discussed as an etiology of PLC.

Antibodies, Monoclonal↗