Mapping QTL associated with resistance to Fusarium head blight in the Nanda2419 x Wangshuibai population. II: type I resistance

Fusarium head blight (FHB) is a serious disease in wheat and barley affecting both yield and quality. To identify genes for resistance to infection, the RIL population derived from 'Nanda2419' x 'Wangshuibai' and the parents were evaluated for percentage of infected spikes (PIS) in four different environments. Using a 2,960 cM marker framework map constructed for this population, ten chromosome regions were detected for their association with type I resistance through interval mapping with Mapmaker/QTL, among which QTLs mapped in the intervals of Xwmc349--Xgwm149 on chromosome 4B, of Xwmc96--Xgwm304 on chromosome 5A and of Xgwm408--Xbarc140 on chromosome 5B were revealed in at least three environments and have Wangshuibai as the source of resistance alleles. Qfhi.nau-4B and Qfhi.nau-5A had larger effects and explained up to 17.5 and 27.0% of the phenotypic variance, respectively. To detect epistasis QTLs, two-locus interactions were examined by whole genome scan. Interactions of five locus pairs were found to have significant effects on type I resistance with the LOD score ranging 3.8-6.5 and four of them conferred resistance in parental phase. The one with the most significant effect was Xcfd42--Xgwm469 (6D)/Xwmc390-2--Xbd04 (2A) pair. No QTL x E interaction was detected for PIS. It was found that flowering time did not have significant effects on PIS in this population. Our studies indicated that Wangshuibai is useful for breeding for both type I and type II scab resistance and the markers associated with the QTLs could be used in marker-assisted selection and isolation of scab-resistance QTLs.

Pharmacological induction of Hsp70 protects apoptosis-prone cells from doxorubicin: comparison with caspase-inhibitor- and cycle-arrest-mediated cytoprotection

Selective modulation of cell death is important for rational chemotherapy. By depleting Hsp90-client oncoproteins, geldanamycin (GA) and 17-allylamino-17-demethoxy-GA (17-AAG) (heat-shock protein-90-active drugs) render certain oncoprotein-addictive cancer cells sensitive to chemotherapy. Here we investigated effects of GA and 17-AAG in apoptosis-prone cells such as HL60 and U937. In these cells, doxorubicin (DOX) caused rapid apoptosis, whereas GA-induced heat-shock protein-70 (Hsp70) (a potent inhibitor of apoptosis) and G1 arrest without significant apoptosis. GA blocked caspase activation and apoptosis and delayed cell death caused by DOX. Inhibitors of translation and transcription and siRNA Hsp70 abrogated cytoprotective effects of GA. Also GA failed to protect HL60 cells from cytotoxicity of actinomycin D and flavopiridol (FL), inhibitors of transcription. We next compared cytoprotection by GA-induced Hsp70, caspase inhibitors (Z-VAD-fmk) and cell-cycle arrest. Whereas cell-cycle arrest protected HL60 cells from paclitaxel (PTX) but not from FL and DOX, Z-VAD-fmk prevented FL-induced apoptosis but was less effective against DOX and PTX. Thus, by inducing Hsp70, GA protected apoptosis-prone cells in unique and cell-type selective manner. Since GA does not protect apoptosis-reluctant cancer cells, we envision a therapeutic strategy to decrease side effects of chemotherapy without affecting its therapeutic efficacy.

Standard treatment for Helicobacter pylori infection is suboptimal in non-ulcer dyspepsia compared with duodenal ulcer in Chinese

BACKGROUND

Recent studies suggest that the Helicobacter pylori eradication rate in patients with non-ulcer dyspepsia is lower when compared to patients with peptic ulcer diseases.

AIM

The aim of this study was to study the efficacy of triple therapy for H. pylori infection in patients with duodenal ulcer vs. patients with non-ulcer dyspepsia.

METHODS

A total of 582 Chinese patients with proven H. pylori infection were recruited to receive: omeprazole 20 mg, amoxicillin 1000 mg and clarithromycin 500 mg all given twice daily for 7 days (OCA regime). Endoscopy with rapid urease test, histology and culture were performed before treatment. Post-treatment H. pylori status was determined by (13)C-urea breath test. Metronidazole, clarithromycin and amoxicillin resistance was defined as minimum inhibitory concentration (MIC) of >8 microg/mL, >1 microg/mL and >1 microg/mL, respectively.

RESULTS

A significantly higher (intention-to-treat/per-protocol) eradication rate was found in patients with duodenal ulcer than those with non-ulcer dyspepsia (91/94% vs. 84/88% respectively, P = 0.011 and P = 0.016). Clarithromycin resistance rate was higher in patients with non-ulcer dyspepsia than those with duodenal ulcer (14% vs. 6%, P = 0.015). Clarithromycin resistance (40% vs. 5%, P < 0.001, OR 12, 95% CI: 5.7-24.3) and the diagnosis of non-ulcer dyspepsia (91% vs. 84%, P = 0.011, OR 2.0, 95% CI: 1.2-3.3) significantly affected the success of H. pylori eradication.

CONCLUSION

Clarithromycin resistance accounts for the significantly lower and suboptimal H. pylori eradication rate of OCA regimen in Chinese patients with non-ulcer dyspepsia compared to those with duodenal ulcer.

Genome-wide analysis of the endothelial transcriptome under short-term chronic hypoxia

We have utilized serial analysis of gene expression (SAGE) to analyze the temporal response of human aortic endothelial cells (HAECs) to short-term chronic hypoxia at the level of transcription. Primary cultures of HAECs were exposed to 1% O2hypoxia for 8 and 24 h and compared with identical same passage cells cultured under standard (5% CO2-95% air) conditions. A total of 121,446 tags representing 37,096 unique tags were sequenced and genes whose expression levels were modulated by hypoxia identified by novel statistical analyses. Hierarchical clustering of genes displaying statistically significant hypoxia-responsive alterations in expression revealed temporal modulation of a number of major functional gene families including those encoding heat shock factors, glycolytic enzymes, extracellular matrix factors, cytoskeletal factors, apoptotic factors, cell cycle regulators and angiogenic factors. Within these families we documented the coordinated modulation of both previously known hypoxia-responsive genes, numerous genes whose expressions have not been previously shown to be altered by hypoxia, tags matching uncharacterized UniGene entries and entirely novel tags with no UniGene match. These preliminary data, which indicate a reduction in cell cycle progression, elevated metabolic stress and increased cytoskeletal remodeling under acute hypoxic stress, provide a foundation for further analyses of the molecular mechanisms underlying the endothelial response to short-term chronic hypoxia.

Apoptosis in non-proliferating cells: implications for viral infection and tumourigenesis

To date much attention has been focused on regulation of apoptosis in proliferating cells. However, recent evidence shows that regulation of apoptosis in quiescent tissue plays an important role in homeostasis of the organism. This review examines the implications of apoptosis of quiescent cells for both tumourigenesis and viral infection such as HIV. In this article we propose a dual role for cellular activation in the homeostasis regulation. In this model cellular mitogens not only activate quiescent cells into the active cell cycle, but under certain conditions, loss of quiescence may result in apoptosis. The loss of quiescence-associated apoptosis may play a significant role in tumourigenesis and viral infections.

[Detection of Toxoplasma infection in women with gynaecologic neoplasms using ELISA]

OBJECTIVE

To understand the concurrent in Toxoplasma infection among women with cervical cancer.

METHODS

The anti-Toxoplasma IgG, IgM antibodies (Abs) and circulating antigens (CAg) in 247 sera (from 50 cases with cervical cancer in group 1, 59 cases with gynaecological benign tumors in group 2 and 138 cases with other diseases in group 3) were detected by ELISA.

RESULTS

The total positive rates of the CAg and the Abs in the three groups were 44.0% (22/50), 25.4% (15/59) and 20.3% (28/138), respectively. The positive rates were 20.0%, 11.9% and 10.9%, respectively for IgG 20.0%, 13.6% and 8.7%, respectively for IgM and 14.0%, 5.1% and 1.4% respectively for CAg.

CONCLUSION

The Toxoplasma infection rate of the cervical cancer group was higher than those of the other two groups, particularly the positive rates of CAg and IgM.

Recurrent genetic alterations in 26 colorectal carcinomas and 21 adenomas from Chinese patients

Colorectal cancer (CRC) is one of the most common malignancies worldwide. The incidence of CRC in the Chinese population has increased dramatically during the last two decades; however, nonrandom chromosomal alterations in Chinese patients have not been described. In the present study, comparative genomic hybridization (CGH) was applied to detect recurrent chromosome alterations in 26 primary colorectal carcinomas and 21 colorectal adenomas from Chinese patients. In CRC, several recurrent chromosomal changes were found, including gains of 8q (14/26 cases, 54%), 20q (54%), 3q (50%), 13q (50%), 5p (46%), 7p (42%), 7q (42%), and 12p (38%) and losses of 18q (65%) and 17p (42%). From comparison with previous CGH studies, the frequent gains of 3q and 12p might be distinctive occurrences in Chinese patients. The distribution of frequently found chromosomal alterations in different locations was studied. The gain of 20q was more frequently found in colon cancer (P<0.01) and the gain of 12p was more frequently found in rectal cancer. Chromosomal alterations were found in 19/21 of adenomas; the most frequent chromosomal alteration was the loss of 18q (9/21 cases, 43%). These recurrent alterations provide several starting points for the isolation of candidate oncogenes and tumor suppressor genes.

Effect of La3+ on the activities of antioxidant enzymes in wheat seedlings under lead stress in solution culture

In order to improve the plant ability to resist lead stress, effect of 0.05 mg/l La(NO3)3 on the activities of catalase (CAT), superoxide dismutase (SOD), the level of malondialdehyde (MDA) in wheat seedlings under lead stress was studied. The effect of La3+ on plant growth, chlorophyll content in wheat seedlings after adding 0, 50, 100 mg/l Pb(NO3)3 to the nutrient solution for 12 days was observed. The plants were grown in nutrient solution in a strictly controlled climate growth room. Effects of La3+ (with La treatment) compared with check groups was evidently observed. The activities of SOD and CAT in root were enhanced 0.45-1.69 times and 33.20-77.77% respectively and MDA content was reduced 11.05-27.49% in root after treatments from the second day till the end of the experiment. The activities of SOD and CAT was found to be increased slightly (P < 0.05) and MDA content decreased in shoot and root of wheat seedlings by La3+ under lead stress within five days after treatments compared with Pbl and Pb2 groups. It was assumed that antioxidant enzymes was found to be increased by La(NO3)3, the antioxidant potential of the wheat seedlings to resist lead stress enhanced. It is suggested that La3+ could be used to resist lead stress at the beginning under stress while the stress was not so serious.

Cytotoxic mono-tetrahydrofuran ring acetogenins from leaves of Annona montana

Further studies on leaves of Annona montana led to isolation of one iso-acetogenin, montanacin G, three pairs of acetogenins, montanacin H-J and 34-epi-montanacin H-J, together with four known acetogenins, gigantetrocins A and B, annonacin and cis-annonacin. Montanacin G belongs to the iso-acetogenin group with a terminal 2,4-trans-ketolactone unit. Montanacin H-J and 34-epi-montanacin H-J contain the rare gamma-hydroxy-gamma-methyl-gamma-lactone moiety. The cytotoxic activities of these compounds, together with previously reported acetogenins, montanacins B and C, were examined against Meth-A and LLC tumor cell lines in vitro.

The role of central arginine vasopressin in corticotropin releasing hormone-induced fever in rats

The purpose of the present study was to investigate the role of central arginine vasopressin (AVP) in corticotropin releasing hormone (CRH) induced fever in the rat. Guide cannulae were inserted into the third ventricle and placed over the ventral septal area (VSA). The content of arginine vasopressin in the VSA of the brain was determined by radioimmunoassay. Colon temperature was monitored in lightly restrained rats by insertion of a catheter mounted thermistor probe 5 cm in the rectum. The results demonstrated that intracerebroventricular (icv) injection of CRH increased AVP level in the VSA and the colonic temperature of the rats. Microinjection of AVP V(1) antagonist into the VSA 10 min before CRH administration significantly enhanced CRH-induced febrile response, while AVP V(1) antagonist itself did not have a significant effect on the colonic temperature. Furthermore, injection of AVP into the VSA 5 min before CRH administration (icv) suppressed the fever evoked by CRH. These findings suggest that CRH is an important factor that stimulates the release of AVP in the VSA during fever, and endogenous AVP in the VSA has an antipyretic action on the CRH-induced fever.

Conjugate addition of arylsilanes to unsaturated carbonyl compounds catalyzed by rhodium in air and water

ArSiCl3 and Ar2SiCl2, believed to be unstable in aqueous media, reacted efficiently with alpha,beta-unsaturated ketones and esters in air and water (in the presence of sodium fluoride and a rhodium catalyst), giving good to excellent yields of the desired conjugate addition products.

Three diterpene glucosides and a diphenylamine derivative from Pieris formosa

Three new diterpenoids, pierisformosides G-I (1-3) and a diphenylamine derivative 4 have been isolated from the ethanol extract of Pieris formosa leaves, compound 1 being a new type seco-ring-A kaurane diterpene glucoside. Their structures were elucidated with the aid of NMR spectroscopy including two-dimensional-NMR techniques.

Promoting mechanism of menthol derivative, 1-O-ethyl-3-buthylcyclohexanol, on the percutaneous absorption of ketoprofen

Menthol derivatives were synthesized and evaluated for their promoting activity on the percutaneous absorption of ketoprofen and skin irritation in vivo, choosing O-ethylmenthol (MET) as the mother compound. The compound having a C-3 positionned n-butyl group (1-O-ethyl-3-n-buthylcyclohexanol, OEBC) indicated the most promoting activity and caused relatively little skin irritation. In order to understand enhancement mechanism of OEBC an in vitro permeation study of ketoprofen was performed. The time course of the cumulative amounts of drug permeated through the rat skin exhibited a linear relation after an initial lag time. This was analyzed in membrane diffusion model and the diffusion and partition parameters of ketoprofen were estimated. Both parameters were remarkably enhanced when a hydrogel containing a small quantity of OEBC (0.5%) was applied. Furthermore, to clarify the site of action of OEBC, we also investigated in vitro permeation study of ketoprofen employing different skins of state, reversed skin and stratum corneum stripped skin. When OEBC was added to the hydrogels which were applied to the reversed and stripped skins, almost no changes of the flux were observed compared with the control (without OEBC). These results suggested that the site of action of OEBC was stratum corneum. Morphological changes of the stratum corneum surface were microscopically observed with 0-2% OEBC. The spaces between the stratum corneum cells treated with 0.5-2% OEBC became extended and the shape of each cell became clear. This may suggest that the site of action of OEBC was the intercellular of stratum corneum. Furthermore, an electron spin resonance study was performed to investigate the effect of OEBC on the intercellular lipid bilayer fluidity of the stratum corneum and the rotational correlation times were calculated. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) were used as the spin label. In use of OEBC, the fluidity of TEMPO labeled the stratum corneum lipid increased as the addition of OEBC. The results suggested that OEBC promote the penetration of drugs by enhancing fluidity of the local lipid bilayers around TEMPO.

Simultaneous optimization based on artificial neural networks in ketoprofen hydrogel formula containing O-ethyl-3-butylcyclohexanol as percutaneous absorption enhancer

The influence of the amounts of additives including 1-O-ethyl-3-n-butylcyclohexanol (OEBC), diisopropyl adipate (DIA), and isopropanol (IPA) on the penetration rate (R(p)) of ketoprofen from hydrogels through rat skin in vivo was investigated. Skin irritation evoked by the application of hydrogels was evaluated based on a microscopic observation of skin cross-sections. Both optimization techniques incorporating an artificial neural network (ANN) and a second-order polynomial regression analysis were applied to the optimization of ketoprofen hydrogel formulations. Findings indicated that the R(p) and total irritation score (TIS) of the skin were predicted quantitatively as a function of quantities of OEBC, DIA, and IPA, employing ANN. In contrast, the prediction ability of the polynomial regression equation was somewhat poorer compared with that of ANN. The observed results of R(p) and TIS in the optimal formulation coincided well with the predictions in the simultaneous optimization technique incorporating ANN.

Novel synthesis of alpha-amino acids via catalysis in air and water

[reaction: see text] A new method was developed for the synthesis of natural and unnatural amino acid derivatives via carbon-carbon bond formation in air and water and at ambient temperature.

Diastereoselective synthesis of polysubstituted tetrahydropyrans and thiacyclohexanes via indium trichloride mediated cyclizations

Polysubstituted tetrahydropyrans and thiacyclohexanes were synthesized in high yields with excellent diastereoselectivities via indium trichloride mediated cyclizations between homoallyl alcohols and mercaptans with aldehydes. In the case of tetrahydropyran products, the stereochemistry of the product was found to be directly correlated with the geometry of the homoallyl alcohols; whereas the cross-cyclization of aldehydes with trans-homoallyl alcohols generated (up-down-up) 2,3,4-trisubstituted tetrahydropyran products exclusively, the reaction of aldehydes with cis-homoallyl alcohols provided mainly (up-up-up) 2,3,4-trisubstituted products. When a trisubstituted homoallyl alcohol was used, its cross-cyclization with aldehydes generated (up-down-up-down-up) pentasubstituted tetrahydropyran derivatives with simultaneous controlling of five stereogenic centers. On the other hand, a cyclization-decyclization equilibrium was observed in the formation of thiacyclohexanes. The reaction of both cis- and trans-homoallyl mercaptans with aldehydes provided the same major diastereomers.

Evaluation and structure-activity relationship of synthesized cyclohexanol derivatives on percutaneous absorption of ketoprofen using artificial neural network

The effect of 35 newly synthesized O-ethylmenthol (MET) derivatives on percutaneous absorption of ketoprofen was investigated in rats. In order to understand the relationship between the structure of compounds and promoting activity (structure-activity relationship), an artificial neural network (ANN) was employed. In the in vivo percutaneous absorption study, male Wistar rats, weighing 160-180 g, were used. The apparent penetration rate (Rp) was estimated based on a pharmacokinetic model with a constant rate of penetration through the skin after a lag time. As an index of the promoting activity of each compound, an enhancement factor (Ef), defined as follows, was used: Ef=Rp(with enhancer)/Rp(without enhancer). An irritation evoked on rat skin was microscopically judged at the end of the in vivo percutaneous absorption experiment and evaluated as a total irritation score (TIS). Ef and TIS were selected as output variables to determine the ANN structure. Calculated logP, molecular weight, steric energy (SE), van der Waals area, van der Waals volume, dipole moment, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were used as factors to determine the structural nature of cyclohexanol derivatives. Among these parameters, logP, SE and LUMO significantly affected the prediction of Ef and TIS. The predicted values of Ef and TIS coincided well with in vivo percutaneous absorption experimental values. However, results observed with a linear regression method were poor compared with the ANN approach. The contribution index of logP was approximately 50% in the prediction of Ef, suggesting that lipophilicity among physicochemical properties contributes most of the promoting activity of these compounds.

Ultrastructural evidence that hippocampal alpha estrogen receptors are located at extranuclear sites

Estrogen may mediate some of its effects on hippocampal function through the alpha isoform of the estrogen receptor (ERalpha). By light microscopy, ERalpha-immunoreactivity (-I) is found in the nuclei of scattered inhibitory gamma-aminobutyric acid (GABA)ergic interneurons. However, several lines of evidence indicate that estrogen also may exert some of its effects through rapid nongenomic mechanisms, possibly by binding to plasma membranes. Thus, to determine whether ERalpha is found in extranuclear sites in the hippocampal formation (HF), four different antibodies to ERalpha were localized by immunoelectron microscopy in proestrous rats. Ultrastructural analysis revealed that in addition to interneuronal nuclei, ERalpha-I was affiliated with the cytoplasmic plasmalemma of select interneurons and with endosomes of a subset of principal (pyramidal and granule) cells. Moreover, ERalpha labeling was found in profiles dispersed throughout the HF, but slightly more numerous in CA1 stratum radiatum. Approximately 50% of the ERalpha-labeled profiles were unmyelinated axons and axon terminals that contained numerous small, synaptic vesicles. ERalpha-labeled terminals formed both asymmetric and symmetric synapses on dendritic shafts and spines, suggesting that ERalphas arise from sources in addition to inhibitory interneurons. About 25% of the ERalpha-I was found in dendritic spines, many originating from principal cells. Within spines, ERalpha-I often was associated with spine apparati and/or polyribosomes, suggesting that estrogen might act locally through the ERalpha to influence calcium availability, protein translation, or synaptic growth. The remaining 25% of ERalpha-labeled profiles were astrocytes, often located near the spines of principal cells. Collectively, these results suggest that ERalpha may serve as both a genomic and nongenomic transducer of estrogen action in the HF.

Potent induction of apoptosis by beta-lapachone in human multiple myeloma cell lines and patient cells

BACKGROUND

Human multiple myeloma (MM) remains an incurable hematological malignancy. We have reported that beta-lapachone, a pure compound derived from a plant, can induce cell death in a variety of human carcinoma cells, including ovary, colon, lung, prostate, pancreas, and breast, suggesting a wide spectrum of anticancer activity.

MATERIALS AND METHODS

We first studied antisurvival effects of beta-lapachone in human MM cells by colony formation assay. To determine whether the differential inhibition of colony formation occurs through antiproliferative activity, we performed MTT assays. The cytotoxicity of beta-lapachone on human peripheral blood mononuclear cells was also measured by MTT assay. To determine whether the cell death induced by beta-lapachone occurs through necrosis or apoptosis, we used the propidium iodide staining procedure to determine the sub-GI fraction, Annexin-V staining for externalization of phosphatidylserine, and fragmentation of cellular genomic DNA subjected to gel electrophoresis. To investigate the mechanism of anti-MM activity, we examined Bcl-2 expression, cytochrome C release, and poly (ADP ribose) polymerase cleavage by Western blot assay.

RESULTS

We found that beta-lapachone (less than 4 microM) inhibits cell survival and proliferation by triggering cell death with characteristics of apoptosis in ARH-77, HS Sultan, and MM.1S cell lines, in freshly derived patient MM cells (MM.As), MM cell lines resistant to dexamethasone (MM.1R), doxorubicin (DOX.40), mitoxantrone (MR.20), and mephalan (LR5). Importantly, after treatment with beta-lapachone, we observed no apoptosis in peripheral blood mononuclear cells in either quiescent or proliferative states, freshly isolated from healthy donors. In beta-lapachone treated ARH-77, cytochrome C was released from mitochondria to cytosol, and poly (ADP ribose) polymerase was cleaved, signature events of apoptosis. Finally, the apoptosis induced by beta-lapachone in MM cells was not blocked by either interleukin-6 or Bcl-2, which confer multidrug resistance in MM.

CONCLUSIONS

Our results suggest potential therapeutic application of beta-lapachone against MM, particularly to overcome drug resistance in relapsed patients.

Diterpenoids from the fruits of Rhododendron molle

Four new diterpenoids, rhodomolleins XV (1), XVI (2), XVII (3), and XVIII (4), together with three known diterpenoids, kalmanol and rhodojaponins III and VI, were isolated from the dried ripe fruits of Rhododendron molle. Their structures were elucidated on the basis of spectroscopic data interpretation.

Diterpene glucosides from Pieris formosa

Five diterpene glucosides, pierisformosides B-F were isolated from Pieris formosa D. Don (Ericaceae). Their structures were elucidated on the basis of spectral analysis. including 1H-1H COSY, 13C-1H COSY, HMBC and NOESY experiments.

The development of algorithms in electrical impedance computerized tomography

Electrical Impedance Computerized Tomography (EICT) is an imaging method to reconstruct the impedance distribution inside of domain through the boundary injected current and display the impedance contrast ratio as an image. This paper concentrates on developing two algorithms to enhance the quality of the conductivity image. The two algorithms are "Fine-Mesh Conversion Method" and "Sub-Domain EICT Method". "Fine-Mesh Conversion Method" is a numerical calibration process to find a coarse mesh impedance network that behaves like a fine mesh network in terms of giving similar voltages under the same current excitations. "Sub-Domain EICT" solves a higher resolution EICT with the cost of a lower resolution EICT by combining "Fine-Mesh Conversion Method", and a Fuzzy Logic Inference Systems (FLIS) classifier.

Selective instability of Orc1 protein accounts for the absence of functional origin recognition complexes during the M-G(1) transition in mammals

To investigate the events leading to initiation of DNA replication in mammalian chromosomes, the time when hamster origin recognition complexes (ORCs) became functional was related to the time when Orc1, Orc2 and Mcm3 proteins became stably bound to hamster chromatin. Functional ORCs, defined as those able to initiate DNA replication, were absent during mitosis and early G(1) phase, and reappeared as cells progressed through G(1) phase. Immunoblotting analysis revealed that hamster Orc1 and Orc2 proteins were present in nuclei at equivalent concentrations throughout the cell cycle, but only Orc2 was stably bound to chromatin. Orc1 and Mcm3 were easily eluted from chromatin during mitosis and early G(1) phase, but became stably bound during mid-G(1) phase, concomitant with the appearance of a functional pre-replication complex at a hamster replication origin. Since hamster Orc proteins are closely related to their human and mouse homologs, the unexpected behavior of hamster Orc1 provides a novel mechanism in mammals for delaying assembly of pre-replication complexes until mitosis is complete and a nuclear structure has formed.