Polyenylphosphatidylcholine attenuates non-alcoholic hepatic fibrosis and accelerates its regression

BACKGROUND/AIMS

Polyenylphosphatidylcholine protects against alcoholic cirrhosis in the baboon. This study assesses whether the antifibrotic effect also pertains to a species other than the baboon and to agents other than alcohol.

METHODS

Rats were injected with either CC14 in peanut oil or peanut oil alone, and pair-fed nutritionally adequate liquid diets, with or without polyenylphosphatidylcholine. Other rats were injected with heterologous albumin instead of CC14. To assess whether polyenylphosphatidylcholine is active on established fibrosis, rats were also given CC14 for 8 weeks, and then divided into two groups and pair-fed a diet with or without polyenylphosphatidylcholine.

RESULTS

After 8 weeks of CC14, the animals were sacrificed; chromotrope aniline blue and Sirius red stains of liver revealed fibrosis or cirrhosis in animals given CC14 alone, whereas the effect was attenuated in the polyenylphosphatidylcholine-supplemented animals. Hepatic collagen content was decreased by 25 to 32% (p < 0.05) and serum ALT and AST were significantly less increased. The expression of liver collagen type I mRNA was significantly increased in CC14 treated rats and was not significantly affected by polyenylphosphatidylcholine although there was a trend towards a lesser increase polyenylphosphatidylcholine also attenuated liver fibrosis produced by the injection of heterologous albumin. CC14-induced liver fibrosis regressed more rapidly in polyenylphosphatidylcholine-treated animals than controls, both histologically and by measurement of collagen (p < 0.05).

CONCLUSIONS

Polyenylphosphatidylcholine (a) attenuates hepatic fibrosis induced by CC14 or human albumin in rats; and (b) accelerates the regression of pre-existing fibrosis.

The role of the four Ca2+ binding sites of troponin C in the regulation of skeletal muscle contraction

In order to study the role of the Ca2+-specific sites (I and II) and the high affinity Ca2+-Mg2+ sites (III and IV) of TnC in the regulation of muscle contraction, we have constructed four mutants and the wild type (WTnC) of chicken skeletal TnC, with inactivated Ca2+ binding sites I and II (TnC1,2-), site III (TnC3-), site IV (TnC4-), and sites III and IV (TnC3,4C-). All Ca2+ binding site mutations were generated by replacing the Asp at the X-coordinating position of the Ca2+ binding loop with Ala. The binding of these mutated proteins to TnC-depleted skinned skeletal muscle fibers was investigated as well as the rate of their dissociation from these fibers. The proteins were also tested for their ability to restore steady state force to TnC-depleted fibers. We found that although the NH2-terminal mutant of TnC (TnC1,2-) bound to the TnC-depleted fibers (with a lower affinity than wild type TnC (WTnC)), it was unable to reactivate Ca2+-dependent force. This supports earlier findings that the low affinity Ca2+ binding sites (I and II) in TnC are responsible for the Ca2+-dependent activation of skeletal muscle contraction. All three COOH-terminal mutants of TnC bound to the TnC-depleted fibers, had different rates of dissociation, and could restore steady state force to the level of unextracted fibers. Although both high affinity Ca2+ binding sites (III and IV) are important for binding to the fibers, site III appears to be the primary determinant for maintaining the structural stability of TnC in the thin filament. Moreover, our results suggest an interaction between the NH2- and COOH-terminal domains of TnC, since alteration of sites I and II lowers the binding affinity of TnC to the fibers, and mutations in sites III and IV affect the Ca2+ sensitivity of force development.

Radioimmunoscintigraphy of gastric adenocarcinomas with 99mTc-chimeric ccM4 antibody

Fourteen patients with gastric lesions were studied for radioimmunoscintigraphy using the 99mTc-ccM4 chimeric antibody reactive with the human tumor-associated TAG72 antigen. These include 10 gastric adenocarcinomas, 3 gastric ulcers and 1 gastric lymphoma. Each patient received an infusion of 30-40 mCi 99mTc-ccM4 antibody. Gamma camera scans were performed at 12-h postadministration. All patients underwent operation after radioimmunoscintigraphy. All surgical specimens including gastric adenocarcinomas, lymphoma and ulcers were confirmed by histopathological studies. The 99mTc-ccM4 antibody was able to detect 6 out of 10 gastric adenocarcinomas (60%) by scans. Its accuracy was even 5 out of 6 (83%) in a group of patients with well/moderately-differentiated adenocarcinomas. In addition to the primary adenocarcinomatous lesions, the 99mTc-ccM4 antibody was also able to detect metastatic lesions in liver and lymph nodes. The smallest adenocarcinomatous lesion detected by scans was about 1 x 1 x 2 cm3. All four patients with gastric ulcers or lymphoma showed negative scan results. Therefore, the chimeric ccM4 antibody may be useful in radioimmunoscintigraphy of gastric adenocarcinomas, especially the well/moderately-differentiated adenocarcinomas.

Phosphorylation-dependent block of cystic fibrosis transmembrane conductance regulator chloride channel by exogenous R domain protein

The cystic fibrosis transmembrane conductance regulator (CFTR) constitutes a linear conductance chloride channel, which is regulated by cAMP-dependent protein kinase phosphorylation at multiple sites located in the intracellular regulatory (R) domain. Studies in a lipid bilayer system, reported here, provide evidence for the control of CFTR chloride channel by its R domain. The exogenous R domain protein (encoded by exon 13 plus 85 base pairs of exon 14) interacted specifically with the CFTR molecule and inhibited the chloride conductance in a phosphorylation-dependent manner. Only the unphosphorylated R domain protein blocked the CFTR channel. Such functional interaction suggests that the putative gating particle of the CFTR chloride channel resides in the R domain.

A cell type-specific enhancer in the human B7.1 gene regulated by NF-kappaB

The costimulatory molecule B7.1 provides a second signal critical for T cell activation. The distribution of this integral membrane protein is restricted to certain tissues where its level of expression is modulated by multiple exogenous stimuli. To identify the molecular basis for specificity and inducibility, the chromatin configuration of the human B7.1 gene was examined in intact nuclei from various cell types. The identification of a tissue-specific deoxyribonuclease I hypersensitive site approximately 3kb upstream of the transcription start site led to the characterization of a cell type-specific enhancer region. This 183-bp region was both cell type specific and responsive to two distinct stimuli, lipopolysaccharide and dibutyryl cAMP, known to regulate B7.1 expression. Deletional and site-directed mutagenesis revealed the presence of multiple functionally critical cis elements within this region, one of which was a nuclear factor (NF)-kappaB consensus sequence. In B7.1-positive B cells, this element bound several members of the NF-kappaB family, transcription factors already implicated in signal transduction pathways relevant to B7.1 expression. This is the first description, to our knowledge, of regulatory elements that control expression of a gene encoding a B7 costimulatory molecule.

Picosecond optical bistability in metallophthalocyanine-doped polymer film waveguides

Ultrafast optical bistability was observed in a planar optical waveguide made with a 2,9,16,23-tetraoctadecanoylamido-substituted vanadyl phthalocyanine-doped polystyrene film. Input-output curves with hysteresis characteristics were measured with laser pulses of 60-ps pulse width at 532 nm. The switchup and switchdown times were less than 10 and 20 ps, respectively. The origin of the nonlinearity giving rise to optical bistability was predominantly electronic effects.

Development and preliminary evaluation of VISLAN, a surgical planning and guidance system using intra-operative video imaging

VISLAN is an integrated neurosurgical planning and guidance system. New segmentation and rendering techniques have been incorporated. A stereo video system is used intra-operatively and fulfils four roles. First, the video display is overlaid with graphical outlines showing the position of the planned craniotomy or the target (enhanced reality displays). Second, a skin surface patch is reconstructed from the stereo video images using patterned light (mean errors of surface point location are < 0.15 mm). Third, a freely mobile, hand-held localizer is tracked in real time (position errors are < 0.5 mm and with improved calibration < 0.2 mm), with its position superimposed on the pre-operative patient representation to assist surgical guidance. Fourth, markers fixed to the skull bone next to the cranial opening are used to detect intra-operative movement and to update registration. Initial results from phantom experiments show an overall system accuracy of better than 0.9 mm for intra-operative localization of features defined in pre-operative images. The prototype system has been tested during six neurosurgical operations with very good results.

The regulatory light chains of myosin modulate cross-bridge cycling in skeletal muscle

We investigated the kinetics of Ca2+ activation of skeletal muscle contraction elicited by the photolysis of caged Ca2+. Previously we showed that partial extraction of the 18-kDa regulatory light chains (RLCs) of myosin decreased the rate of force development and was subsequently increased by approximately 20% following reconstitution with RLCs (Potter, J. D., Zhao, J. and Pan, B. S. (1992) FASEB J. 6, A1240). We extend here the RLC-extraction study to the complete removal of the RLCs. The complete removal of RLCs was achieved by a combination of 5,5'-dithiobis-(2-nitrobenzoic acid) and EDTA treatment followed by reduction of oxidized sulfydryl groups by dithiothreitol. Under these conditions the complete extraction of RLCs was accompanied by the extraction of endogenous troponin C, resulting in the loss of isometric tension. Steady state force was restored to 65-75% following troponin C reconstitution and increased to 75-85% as a result of RLC reincorporation into the fibers. The rates of force transients generated by UV-flash photolysis of 1-(2-nitro-4,5-dimethoxyphenyl)-N,N,N',N' -tetrakis[(oxycarbonyl)methyl]-1,2-ethanediamine) or nitrophenyl-EGTA, photoliberating bound Ca2+, decreased 2-fold after RLC extraction and troponin C reconstitution and then increased to the values of intact fibers after RLC reconstitution. These results support our earlier findings that the regulatory light chains of myosin play an important role in the kinetics of cross-bridge cycling.

Slow conversions among subconductance states of cystic fibrosis transmembrane conductance regulator chloride channel

The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel exhibits multiple subconductance states. To study the regulation of conductance states of the CFTR channel, we expressed the wild-type CFTR protein in HEK 293 cells, and isolated microsomal membrane vesicles for reconstitution studies in lipid bilayer membranes. A single CFTR channel had a dominant conductance of 7.8 pS (H), plus two sub-open states with conductances of approximately 6 pS (M) and 2.7 pS (L) in 200 mM KCl with 1 mM MgCl2 (intracellular) and 50 mM KCl with no MgCl2 (extracellular), with pH maintained at 7.4 by 10 mM HEPES-Tris on both sides of the channel. In 200 mM KCl, both H and L states could be measured in stable single-channel recordings, whereas M could not. Spontaneous transitions between H and L were slow; it took 4.5 min for L-->H, and 3.2 min for H-->L. These slow conversions among subconductance states of the CFTR channel were affected by extracellular Mg; in the presence of millimolar Mg, the channel remained stable in the H state. Similar phenomena were also observed with endogenous CFTR channels in T84 cells. In high-salt conditions (1.5 M KCl), all three conductance states of the expressed CFTR channel, 12.1 pS, 8.2 pS, and 3.6 pS, became stable and seemed to gate independently from each other. The existence of multiple stable conductance states associated with the CFTR channel suggests two possibilities: either a single CFTR molecule can exist in multiple configurations with different conductance values, or the CFTR channel may contain multimers of the 170-kDa CFTR protein, and different conductance states are due to different aggregation states of the CFTR protein.

Enhancement of antiproliferative activity of 1alpha,25-dihydroxyvitamin D3 (analogs) by cytochrome P450 enzyme inhibitors is compound- and cell-type specific

Ketoconazole (keto) or liarozole (liaro), inhibitors of the cytochrome P450 enzymes that mediate vitamin D and A hydroxylations, could potentiate the antiproliferative effects of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and its analogs. Proliferation of MCF-7 and T47-D human breast cancer cells, MG-63 human osteosarcoma cells and HL-60 human promyeloid leukemia cells was concentration dependently inhibited by 1alpha,25(OH)2D3. The vitamin D analogs KH 1060 [20-epi-22-oxa-24,26,27-trihomo-1alpha,25(OH)2D3], RO 23-6010 [16-ene-23-yne-26-trifluoro-1,25(OH)2D2D3], ZXY 835 [20-epi-23-yne-25,26-epoxy-1alpha(OH)D3], and CD 99 [11alpha-methyl-1alpha,25(OH)2D3] were 150-,58-,16- and 7-fold more potent than 1alpha,25(OH)2D3 in inhibiting the proliferation of MCF-7 cells, respectively. A similar rank order of potency was observed in other cell lines. The antiproliferative effects of the vitamin D hormone and analogs was enhanced in MCF-7 cells when coincubated with 1 microM keto (7-, 10-, 5-, 25- and 1.3-fold more potent than in the absence of keto), respectively. The antiproliferative effect was less enhanced when 1alpha,25(OH)2D3 or its analogs KH 1060, ZXY 835 and RO 23-6010 were combined with liaro (3-, 7-, 2- and 3-fold, respectively). Keto and liaro did not markedly potentiate the activity of 1alpha,25(OH)2D3 or its analogs in MG-63 or HL-60 cells. These results suggest that differences in cellular metabolism can at least partially explain the different potency of vitamin D analogs. Moreover, the metabolism of vitamin D analogs is cell-type specific.

Interaction between photosystem I and flavodoxin from the cyanobacterium Synechococcus sp. PCC 7002 as revealed by chemical cross-linking

The interaction between photosystem I (PS I) and flavodoxin from the cyanobacterium Synechococcus sp. PCC 7002 was investigated by covalent cross-linking in the presence of a hydrophilic cross-linker, N- ethyl-3-(3-diaminopropyl)carbodiimide. Under the experimental conditions employed, five distinct cross-linking products of flavodoxin and PS I subunits are formed. Immunoblot analyses show that these species are the result of cross-linking of flavodoxin to PsaC, PsaD, an unidentified low-molecular-mass PS I polypeptide, and a 15-kDa subunit. The latter has been indirectly identified as the PsaF subunit. Analysis of the interaction of flavodoxin with PS I from a psaE mutant indicates that the PsaE subunit is required for correct complex formation between flavodoxin and PS I, although this subunit is not directly cross-linked to flavodoxin. In addition, the cross-linking products of PsaD with PsaC and PsaL, and PsaE with PsaF, are observed. The covalent complex of flavodoxin and PS I is shown to be fully inhibited with respect to electron transfer to soluble flavodoxin, ferredoxin or ferredoxin:NADP+ oxidoreductase.

Effects of low-dose long-term sodium fluoride preventive treatment on rat bone mass and biomechanical properties

Effects of fluoride on bone strength and cortical bone mass remain controversial. We compared 9-month, low-dose sodium fluoride (NaF) treatment with estrogen replacement therapy. Female Wistar rats 4.5 months old were divided into baseline, sham-operated (sham), sham-treated with NaF at 0.5 mg NaF/kg/day in drinking water, and ovariectomy (OVX), OVX treated with NaF and with estrogen. Bone mass was measured by dual X-ray absorptiometry (DXA) in vitro. Dimensions of the first lumbar vertebral body (L1) were determined by radiogrammetry. The right femur was processed undecalcified to obtain a midshaft cross-section to determine cross-sectional moments of inertia (CSMIs). L1 compressive test and left femoral torsional test were performed. OVX induced significant bone loss in L1 and femoral midshaft. Bone mass was increased to a greater extent in NaF-treated rats than in rats receiving estrogen replacement therapy. Femoral CSMIs in OVX rats, both L1 sizes and femoral CSMIs in NaF-treated rats, were significantly increased. Estrogen treatment had the least dimension expansion. OVX significantly decreased L1 compressive variables. There was no statistical difference in compressive parameters between NaF-treated groups and controls. OVX significantly increased femoral torsional strength but NaF treatment did not. Bone fluoride content was significantly increased after treatment with NaF. No significant difference in bone mineralization degree (ash and calcium) was found between treated and control rats. The discrepancy that an increase in bone mass and geometric properties in both trabecular and cortical bones by low-dose, long-term NaF treatment did not increase vertebral strength nor proportionally improve femoral strength indicated that the bone intrinsic biomechanical properties could be changed by NaF treatment.

Craniotomy guidance using a stereo-video-based tracking system

In open intracranial neurosurgery, it is desirable to minimize exposure and to approach the target in the most accurate way possible. The VISLAN system described here employs a completely passive hand-held locator which is tracked by a video system and does not require a mechanical linkage nor cables. The system also tracks easily recognizable, constant, anatomical landmarks of the patient. By this means the initial registration of pre-operative imaging and the detection of, and correction for, patient movement can be accomplished. High-resolution MRI segmented interactively is used to define external surface and brain anatomy. Thus, a pre-operative patient representation (POPR) is planned. During the surgical procedure the patient's head is illuminated by structured light and stereo-video pictures obtained from two television cameras mounted above the head. The system is calibrated and registered with the POPR using a chamfered matching algorithm. The locator is also tracked in space by the video system, and its tip position shown in relation to the POPR on the video monitor.

Structure-function relationships of the complement regulatory protein, CD59

CD59 (membrane inhibitor of reactive lysis, protectin) is a membrane protein whose functions include the inhibition of the insertion of the ninth component of complement into the target membrane. It belongs to a superfamily of proteins including Ly-6, elapid snake venom toxins, and urokinase receptor (UPAR); the members of the superfamily have a similar structure that includes four (in mammals five) disulfide bridges that maintain a three-dimensional conformation consisting of a central core, three finger-like "loops" extending from it and a small loop near the coboxyl end. We have used site directed mutagenesis to explore three aspects of the structure of CD59: 1) the role of the disulfide bridges in expression and function of the molecule; 2) the location of epitopes reacting with monoclonal antibodies to the molecule; and 3) the parts of the molecule that are critical to its function in inhibiting complement lysis. Mutant molecules in which the disulfides maintaining the finger-like loops (Cys3-Cys26, Cys19-Cys39, and Cys45-Cys63) were removed were not expressed on the cell surface. The mutation of the disulfide (Cys6-Cys13) resulted in no change in expression or function. The mutation of Cys64-Cys69 maintaining the small loop resulted in an expressed molecule with increased functional activity. The major epitope for 6 of 7 monoclonal antibodies was centered on Arg53 as the mutation 53Arg-->Ser resulted in a loss of interaction with these antibodies, as did the deletion of four nearby residues (Leu54-Asn57). The alteration 55Arg-->Ser resulted in loss of reactivity for some but not other antibodies. The reactivity with one monoclonal antibody, H19, was abrogated by the mutations 61Tyr-->Gly and 61Tyr-->Ala. Functional activity of the molecule was not adversely altered by mutations in the first and second loops; however, the 61Tyr-->Gly mutation was non-functional. The mutation of 61Tyr-->His diminished function but changes 61Tyr-->Ala and 61Tyr-->Phe had no effect on function. We conclude that the functional site of CD59 is located in this region of the molecule.

Nonhypercalcemic vitamin D analogs: interactions with the vitamin D-binding protein

The natural vitamin D hormone, 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3), not only regulates serum and bone calcium homeostasis but is probably also a paracrine factor in several cells and tissues including skin, immune system, placenta and brain, where it stimulates cell differentiation and inhibits cell proliferation. Several structural analogs of 1 alpha, 25-(OH)2D3 not only have superagonist activity but also display a selective action profile: indeed they maintain or have increased activity on cell differentiation/proliferation but also have substantially decreased calcemic activity when compared to 1 alpha,25-(OH)2D3. This decreased calcemic activity is partially due to mere pharmacological reasons: because of low binding affinity for the plasma vitamin D-binding protein, a more rapid extracellular metabolism and increased cellular uptake is possible when compared to 1 alpha,25-(OH)2D3. Their short extracellular half-life combined with comparable or enhanced transactivation potency together with analog-and cell-type-specific intracellular metabolism can probably explain why some analogs have a unique combination of superagonist activity and specific action profile with favorable dissociation of differentiation versus calcemic potency.

Phosphorylation of both serine residues in cardiac troponin I is required to decrease the Ca2+ affinity of cardiac troponin C

The phosphorylation of cardiac muscle troponin I (CTnI) at two adjacent N-terminal serine residues by cAMP-dependent protein kinase (PKA) has been implicated in the inotropic response of the heart to beta-agonists. Phosphorylation of these residues has been shown to reduce the Ca2+ affinity of the single Ca(2+)-specific regulatory site of cardiac troponin C (CTnC) and to increase the rate of Ca2+ dissociation from this site (Robertson, S. P., Johnson, J. D., Holroyde, M. J., Kranias, E. G., Potter, J. D., and Solaro, R. J. (1982) J. Biol. Chem. 257, 260-263). Recent studies (Zhang, R., Zhao, J., and Potter, J. D. (1995) Circ. Res. 76, 1028-1035) have correlated this increase in Ca2+ dissociation with a reduced Ca2+ sensitivity of force development and a faster rate of cardiac muscle relaxation in a PKA phosphorylated skinned cardiac muscle preparation. To further determine the role of the two PKA phosphorylation sites in mouse CTnI (serine 22 and 23), serine 22 or 23, or both were mutated to alanine. The wild type and the mutated CTnIs were expressed in Escherichia coli and purified. Using these mutants, it was found that serine 23 was phosphorylated more rapidly than serine 22 and that both serines are required to be phosphorylated in order to observe the characteristic reduction in the Ca2+ sensitivity of force development seen in a skinned cardiac muscle preparation. The latter result confirms that PKA phosphorylation of CTnI, and not other proteins, is responsible for this change in Ca2+ sensitivity. The results also suggest that one of the serines (23) may be constitutively phosphorylated and that serine 22 may be functionally more important.

Regulation of transforming growth factor beta receptors in H-ras oncogene-transformed rat intestinal epithelial cells

We have reported that over expression of the H-ras oncogene causes resistance to growth inhibition by transforming growth factor beta 1 (TGF-beta 1) and a time-dependant switch of type II to type I TGF-beta receptor expression in the rat intestinal epithelial cell line IEC-18 (J. Filmus, J. Zhao, and R. N. Buick, Oncogene, 7: 521-526, 1992). Here, we investigate the possible mechanisms involved in H-ras-mediated regulation of TGF-beta receptors in an IEC-18 cell clone expressing H-ras, conditional on the activity of a dexamethasone-sensitive promoter. The switch from type II to type I receptor expression in response to H-ras expression has a requirement for de novo RNA synthesis. In addition, accumulation of TGF-beta receptor type II mRNA is approximately 5-fold lower in ras-expressing cells compared to control cells. Nuclear run-on experiments suggest that the down-regulation of type II receptor mRNA by H-ras oncogene is based, at least in part, on reduced transcription. We have also analyzed the consequences of H-ras expression on the properties of the TGF-beta receptors. Type I and II in IEC-18 cells and type I receptors in ras-transformed cells have similar characteristics in terms of binding affinities for TGF-beta 1 (or TGF-beta 2) turnover rates and glycosylation states. Notably, the type I receptors in ras-transformed cells are not capable of ligand-induced internalization. Although H-ras expression in IEC-18 cells causes resistance to TGF-beta-mediated growth inhibition, the cells remain responsive to TGF-beta 1 stimulation of fibronectin expression. These results are discussed in the context of the knowledge of TGF-beta receptor complexity and signal transduction, and with reference to the potential role for loss of TGF-beta-mediated negative growth regulation in malignant transformation.

Rectification of skeletal muscle ryanodine receptor mediated by FK506 binding protein

The cytosolic receptor for immunosuppressant drugs, FK506 binding protein (FKBP12), maintains a tight association with ryanodine receptors of sarcoplasmic reticulum (SR) membrane in skeletal muscle. The interaction between FKBP12 and ryanodine receptors resulted in distinct rectification of the Ca release channel. The endogenous FKBP-bound Ca release channel conducted current unidirectionally from SR lumen to myoplasm; in the opposite direction, the channel deactivated with fast kinetics. The binding of FKBP12 is likely to alter subunit interactions within the ryanodine receptor complex, as revealed by changes in conductance states of the channel. Both on- and off-rates of FKBP12 binding to the ryanodine receptor showed clear dependence on the membrane potential, suggesting that the binding sites of FKBP12 reside in or near the conduction pore of the Ca release channel. Rectification of the Ca release channel would prevent counter-current flow during the rapid release of Ca from SR membrane, and thus may serve as a negative feedback mechanism that participates in the process of muscle excitation-contraction coupling.

The synthesis of blocked triplet-phosphoramidites and their use in mutagenesis

A general approach for the synthesis of oligonucleotide-triplet phosphoramidites and the synthesis of four such blocks are described. A strategy was devised to minimize the number of dimer precursors needed for synthesis of a complete set of triplet-amidite blocks encoding all 20 amino acids. Whereas synthesis of 20 triplet-amidite blocks consisting of codon sequences requires 16 dimer blocks, just seven dimer blocks are required to synthesize all required antisense sequences. The antisense sequences are then converted to codons in template mediated replication. Using a mixture of four triplet-amidites and conventional automated solid-phase DNA synthesis, short (6mer) and medium length (30mer) oligonucleotide mixtures were synthesized and analyzed. The latter was replicated in vitro and used as a mutagenic cassette to produce four mutants of Asp 221 in the enzyme thymidylate synthase. The method establishes the direction and utility for the production and use of triplet-amidite blocks in DNA synthesis.

Modified ligands to FA and FB in photosystem I. I. Structural constraints for the formation of iron-sulfur clusters in free and rebound PsaC

Cysteines 14, 21, 34, 51, or 58 in PsaC of photosystem I (PS I) were replaced with aspartic acid (C21D and C58D), serine (C14S, C34S, and C51S), and alanine (C14A, C34A, and C51A). When free in solution, the C34S and C34A holoproteins contained two S = 1/2 ground state [4Fe-4S] clusters; all other mutant proteins contained [3Fe-4S] clusters and [4Fe-4S] clusters; in addition, there was evidence in C14S, C51S, C14A, and C51A for high spin (S = 3/2) [4Fe-4S] clusters, presumably in the modified site. These findings are consistent with the assignment of C14, C21, C51, and C58, but not C34, as ligands to FA and FB. The [4Fe-4S] clusters in the unmodified sites in C14S, C51S, C14A, and C51A remained highly electronegative, with Em values ranging from -495 to -575 mV. The [3Fe-4S] clusters in the modified sites were driven 400 to 450 mV more oxidizing than the native [4Fe-4S] clusters, with Em values ranging from -98 mV to -171 mV. A C14D/C51D double mutant contains [3Fe-4S] and S = 1/2 [4Fe-4S] clusters, showing that the 3Cys.1Asp motif is also able to accommodate a low spin cubane. When C34S, C34A, C14S, C51S, C14A, and C51A were rebound to P700-FX cores, electron transfer to FA/FB was regained, but functional reconstitution has not yet been achieved for C21D, C58D, or C14D/C51D. These data imply that PsaC requires two iron-sulfur clusters to refold, one of which must be a cubane. Since two [4Fe-4S] clusters are found in all reconstituted PS I complexes, the presence of two cubanes in free PsaC may be a necessary precondition for binding to P700-FX cores.

Arabidopsis thaliana tryptophan synthase alpha: gene cloning, expression, and subunit interaction

The tryptophan synthase alpha subunit catalyzes the conversion of indole-3-glycerolphosphate to indole, the penultimate reaction in the biosynthesis of the essential amino acid tryptophan. A cDNA encoding Arabidopsis thaliana tryptophan synthase alpha(TSA1) was isolated by complementation of an Escherichia coli delta trpA mutation and by polymerase chain reaction amplification from a cDNA library using degenerate primers. A TSA1 genomic clone was also isolated and 5 kb of the DNA sequence determined. A single sequence in the Arabidopsis genome with homology to the TSA1 cDNA was detected by high-stringency genomic Southern blot hybridization. In contrast under hybridization conditions of reduced stringency, one or two additional homologous sequences were observed. A 1.4 kb transcript was detected in wild-type RNA with the TSA1 cDNA as a probe. Several lines of evidence, including immunoaffinity chromatography, suggest that the active A. thaliana tryptophan synthase enzyme consists of a heterosubunit complex, presumably analogous to the prokaryotic alpha 2 beta 2 complex. Immunoblot analysis indicated that the plant alpha and beta subunits are present throughout development.

Darwin's selection within the human body

It has been widely accepted that Darwin's natural selection plays a basic role in carcinogenesis and some other disease processes, but is not relevant to the normal multicellular life within the human body. The hypothesis proposed here is that selection and other evolutionary mechanisms not only normally or physiologically exist within the body of human beings and other multicellular organisms, but also persist and 'function' throughout the entire life span of the organism, from the embryo development to the aging process. This is based on the concept of cell individuality and the fact that there are a great deal of variations in cell populations, in particular possible existence of somatic genetic variations within the body. To realize the existence of natural selection in the multicellular life and study how it operates within organisms in both physiological and pathological conditions are fundamentally important to our understanding of human biology and medicine.

Light-induced noncentrosymmetry in acceptor-donor-substituted azobenzene solutions

Light-induced noncentrosymmetry was achieved experimentally in acceptor-donor-substituted azobenzene solutions and observed by phase-matched nondegenerate six-wave mixing. The microscopic origin of the induced noncentrosymmetry was found to be orientational hole burning, which was distinguished directly with net orientation of molecules by experimental observations. The decay time of the induced noncentrosymmetry depended on the rotational orientation time of the sample's molecule, which varied linearly with the viscosity of the solvent.

[Investigation of the application of electrical impedance principle for the diagnosis of diaphragm fatigue]

We designed and performed the chest and abdomen impedance respirograph (IRG), which included the one dimentional IRG and the two dimentional IRG, by applying the principle of bioelectrical impedance. Using IRG, we measured the non-synchronized chest and abdomen respiratory motions occurring in the diaphragmatic fatigue. The results showed that all 203 normal control subjects showed synchronized pattern of chest and abdomen respiratory motions. In 189 COPD patients 117 (61.9%) showed non-synchronized respiratory motions which could be further divided into three types: type I showed complete contradirectional movements of respiration, M > 24% and alpha angle > 120 degrees; type II showed staggered peak of the chest and abdomen motion curves, 13% < M < 24%, 50 degrees < alpha angle < 120 degrees; type III showed double peaks in the one dimentional IRG and 8-shaped double circles in the two dimentional IRG, M < 13%, alpha angle > 40 degrees. When compared with Pdi and diaphragm myoelectricity frequency spectrum the rates of accordance were 81.8% and 90%, respectivity, suggesting that IRG could be reliably used to diagnose diaphragmatic fatigue. This technique is simple, easy, cheap and non-invasive. It is, therefore, worth to be widely recommanded for clinical investigation.

Mechanisms of conduction time hysteresis in rabbit atrioventricular node

The functional origin of atrioventricular nodal hysteresis was studied in isolated rabbit heart preparations. This hysteresis is characterized by asymmetric changes in nodal conduction time (NCT) occurring for symmetric changes in cycle length. The respective contribution of the nodal properties of recovery, facilitation, and fatigue to the beat-to-beat changes in NCT observed during paired symmetric ramps of decreasing and increasing cycle length was determined with specifically design stimulation protocols. Nodal hysteresis was found to be entirely accounted for by variations in the contribution of nodal recovery and fatigue properties observed at corresponding cycle lengths. The study establishes how this contribution varies on a beat-to-beat basis as a result of cycle length history. This holds true for the numerous changes in hysteresis observed in response to changes in the sequence and slope of the ramps. Facilitation clearly affected NCT during these responses but did not contribute to the hysteresis. Moreover, the study demonstrates that there is no inherent change in the characteristics of nodal function with the direction of the ramp that could account for the hysteresis. Thus nodal hysteresis arises from nodal functional properties of recovery and fatigue but does not constitute a distinct independent intrinsic property of the node.

The rise and prospects of medical aesthetics

Since the 1980s, Chinese scholars have been trying to expound and synthetise elementary aesthetical ideas which occur in medicine, in order to treat this area of study as a defined branch of medicine--'medical aesthetics'. It is in this context that the points discussed in this paper arise. We set forth in detail the ideas, objectives and methods adopted within the framework of medical aesthetics and its applied branch--medical cosmetology and expound the relations between them. We think the task of medical aesthetics is to study the human body in its entirety, concentrating on both internal and external beauty and put the findings into practice, whereas the task of medical cosmetology is to study and assess only the external beauty of the human body and to take action on that basis. Medical cosmetology is the enforcement of medical aesthetics, practised in order to give positive results connected with physical beauty, and is therefore easily understood by the layman. It is known that the development of medical cosmetology represents an important breakthrough in the development of medical aesthetics. We think that beauty should not be measured mechanically, always following the same pattern, but that it should be considered individually with everyone's own particular characteristics. The quality of physical attractiveness should be assessed jointly by the doctor and his patient or client, not solely by either of these individuals nor even by a group of doctors.(ABSTRACT TRUNCATED AT 250 WORDS)

The complex of phosphatidylinositol 4,5-bisphosphate and calcium ions is not responsible for Ca2+-induced loss of phospholipid asymmetry in the human erythrocyte: a study in Scott syndrome, a disorder of calcium-induced phospholipid scrambling

Elevation of cytoplasmic Ca2+ levels in human erythrocytes induces a progressive loss of membrane phospholipid asymmetry, a process that is impaired in erythrocytes from a patient with Scott syndrome. We show here that porcine erythrocytes are similarly incapable of Ca2+-induced redistribution of membrane phospholipids. Because a complex of phosphatidylinositol 4,5-bisphosphate (PIP2) and Ca2+ has been proposed as the mediator of enhanced transbilayer movement of lipids (J Biol Chem 269:6347,1994), these cell systems offer a unique opportunity for testing this mechanism. Analysis of both total PIP2 content and the metabolic-resistant pool of PIP2 that remains after incubation with Ca2+ ionophore showed no appreciable differences between normal and Scott erythrocytes. Moreover, porcine erythrocytes were found to have slightly higher levels of both total and metabolic-resistant PIP2 in comparison with normal human erythrocytes. Although loading of normal erythrocytes with exogenously added PIP2 gave rise to a Ca2+-induced increase in prothrombinase activity and apparent transbilayer movement of nitrobenzoxadiazolyl (NBD)-phospholipids, these PIP2-loaded cells were also found to undergo progressive Ca2+-dependent cell lysis, which seriously hampers interpretation of these data. Moreover, loading Scott cells with PIP2 did not abolish their impaired lipid scrambling, even in the presence of a Ca2+-ionophore. Finally, artificial lipid vesicles containing no PIP2 or 1 mole percent of PIP2 were indistinguishable with respect to transbilayer movement of NBD-phosphatidylcholine in the presence of Ca2+. Our findings suggest that Ca2+-induced redistribution of membrane phospholipids cannot simply be attributed to the steady-state concentration of PIP2, and imply that such lipid movement is regulated by other cellular processes.

[Multimodality therapy of late stage lung cancer]

A prospective randomized study of 80 cases of stage III lung cancer treated with different multimodality therapy was carried out. Life table and Kaplan-Meir curve were employed to calculate survival rate. Log rank-multivariate analysis and time t test were used to evaluate statistical values of the 80 cases, 40 SCLC were randomly treated with either chemotherapy (CT)-surgery-CT or CT-radiotherapy (RT)-CT. The year survival rates were better in the group treated with CT-surgery-CT, a statistical difference was observed in 2yr survival rate (P < 0.05). Thus, surgical resection for SCLC was better than RT after CT. The remaining 40 cases of NSCLC were randomly treated with either CT-RT-CT or RT-CT. Multivariate analysis showed a better statistical meaning in the 20 cases treated with CT-RT-CT than the other group, their 1, 2 year survival rates were 27%, 40% and 22%, 15%, respectively. Thus preradiative CT was beneficial for survival.

Effect of anthrax toxin's lethal factor on ion channels formed by the protective antigen

Protective antigen (PA), a component of anthrax toxin, mediates translocation of the toxin's lethal and edema factors (LF and EF, respectively) to the cytoplasm, via a pathway involving their release from an acidic intracellular compartment. PA63, a 63-kDa proteolytic fragment of PA, can be induced to form ionconductive channels in the plasma membrane of mammalian cells by acidification of the medium. These channels are believed to be comprised of dodecyl sulfate-resistant oligomers (heptameric rings) of PA63 seen by electron microscopy of the purified protein. Here we report that the PA63-mediated efflux of 86Rb+ from preloaded CHO-K1 cells under acidic conditions is strongly inhibited (> or = 70%) by LF or LFN, a PA-binding fragment of LF. Control proteins caused no inhibition. Evidence is presented that the inhibition involves partial blockage of ion conductance by the PA63 channel. Also, oligomer formation is slowed somewhat by LF at pH values near the pH threshold of channel formation (pH approximately 5.3), suggesting that channel formation may also be retarded under these conditions. The relevance of these results to the location of the LF-binding site on PA63 and the mechanism of LF and EF translocation is discussed.

Inhibitory action of metabolites of Pseudomonas aeruginosa against gram-negative bacteria

Fifty clinical isolates of Pseudomonas aeruginosa were tested for inhibition of growth of clinical isolates of Escherichia coli, Salmonella infantis, Klebsiella pneumoniae and other Gram-negative bacteria in the authors' laboratory. Pseudomonas aeruginosa was strongly active against both E. coli and Enterobacter cloacae, with 89.4% and 94.7% inhibition respectively, but weakly active against S. infantis, K. pneumoniae and Proteus mirabilis with 56.3%, 48.8% and 23.8% inhibition, respectively. The pigmented strains were found to have stronger antimicrobial activity than the unpigmented strains. Pyocyanin, the major metabolite of Pseudomonas aeruginosa, has been shown to inhibit Escherichia coli, Proteus spp. and other Gram-negative bacteria, by research with a few strains of P. aeruginosa and a single inhibited strain. However, little attempt has been made to determine the inhibitory action of many strains of P. aeruginosa against a large number of clinical isolates such as Escherichia spp., Klebsiella spp., and Salmonella spp., up to now. For this reason, in this study we examined 50 randomly selected clinical isolates of P. aeruginosa for inhibition of growth of a wide range of Gram-negative bacteria, including 30 strains of E. coli, 30 of K. pneumoniae, 30 of S. infantis, 6 of Enterobacter cloacae and 9 of Proteus mirabilis.

[Postoperative residual intracranial aneurysms]

From January 1991 to 1994, 99 aneurysms in 91 patients were clipped in the Neurosurgy Department of Beijing Tiantan Hospital. Six residual aneurysms were found by postoperative angiography. We analyzed these patients and concluded that the occurrence of residual aneurysms depends mainly on the location, size, type, neck width of the aneurysms, and their rupture during operation. According to this, we give opinions on how to prevent residual aneurysms and how to deal with them.

Antagonistic activity of 24-oxa-analogs of vitamin D

24-Oxa-vitamin D3 (24-oxa-D3) and 24-oxa-1 alpha-hydroxyvitamin D3 were designed as possible inhibitors of the vitamin D metabolic activation pathway. Their affinity for the vitamin D receptor (from pig intestine) and human vitamin binding protein were reduced, and their potency to induce cell differentiation of human leukemia cells (HL 60) or osteosarcoma cells (MG 63) was markedly reduced (19% and 3%, respectively), in comparison with calcitriol. A single or chronic injection of 24-oxa-D3 had no biological activity, whereas chronic administration of 24-oxa-1 alpha-hydroxy-D3 showed weak agonist activity in rachitic chicks. When the 24-oxa-D3 was given prior to a single injection of vitamin D3, lower values of serum calcium (64% of the value obtained in vitamin D-treated animals), osteocalcin (52%), 25-(OH)D3 (45%) and duodenal calbindin-D 28K (9.4%) were found. When given chronically in a 100-fold more excess no clear antagonistic effects were observed. 24-Oxa-D3 is thus a new metabolic weak antagonist of vitamin D3, but adding a hydroxyl group at C-1 creates a weak agonist.

Cardiac troponin I phosphorylation increases the rate of cardiac muscle relaxation

Cardiac troponin (Tn) I (CTnI), compared with skeletal TnI, contains extra amino acids (32 to 33) at its amino terminus, including two adjacent serine residues. These two serine residues are believed to be phosphorylated by protein kinase A (PKA) upon stimulation of the heart by beta-agonists. In this study, we found that phosphorylation of a cardiac skinned muscle preparation by PKA, mainly at CTnI, results in a decrease in the Ca2+ sensitivity of muscle contraction. The pCa50 decreased by approximately 0.27 +/- 0.06 pCa units upon phosphorylation. To study cardiac muscle relaxation, we used diazo-2, a photolabile Ca2+ chelator with a low Ca2+ affinity in its intact form that is converted to a high-affinity form after photolysis. We found that the rate of cardiac muscle relaxation increased from a time of half-relaxation (t1/2) = 110 +/- 10 milliseconds to t1/2 = 70 +/- 8 milliseconds after CTnI phosphorylation. This result demonstrates that CTnI phosphorylation can be linked with the increased rate of muscle relaxation in a relatively intact muscle preparation. Since CTnI phosphorylation has been shown previously to affect the Ca2+ affinity and Ca2+ off-rate of CTnC in vitro, it is likely that the faster relaxation seen here reflects faster dissociation of Ca2+ from cardiac TnC (CTnC). Model calculations show that increased dissociation of Ca2+ from CTnC, coupled with the faster uptake of Ca2+ by the sarcoplasmic reticulum stimulated by PKA phosphorylation of phospholamban, can account for the faster relaxation seen in the inotropic response of the heart to catecholamines.

Trypanosoma brucei dihydrofolate reductase-thymidylate synthase: gene isolation and expression and characterization of the enzyme

The gene encoding the bifunctional dihydrofolate reductase (DHFR) and thymidylate synthase (TS) of Trypanosoma brucei brucei has been isolated and expressed in Escherichia coli, and the enzyme has been purified and characterized. The coding sequence of the DHFR-TS is 1581 nt, encoding a 527-amino-acid protein of 58,505 Da. The gene was expressed under control of the trc promoter in pKK233-2. The resulting expression plasmid conferred trimethoprim resistance to E. coli DH5 alpha and complemented the TS deficiency in chi 2913recA cells indicating the presence of active DHFR and TS. DHFR-TS was purified by methotrexate-Sepharose chromatography. In addition to the full-length enzyme, the purified enzyme contained 31 and 31.5-kDa forms of the enzyme that cross-reacted with anti-L. major DHFR-TS antibodies; one was truncated at the N- and C termini, and the other at only the C terminus. Despite the presence of sufficient TS for complementation, TS activity was not detectable in the crude extract or in the final purified enzyme preparation. Although the majority of the enzyme appears to be full length, it is possible that the TS domain has been degraded by one of more residues, which would inactivate the ability to synthesize thymidylate. Kinetic analysis of DHFR yielded kcat and Km values similar to those of related enzymes. The T. brucei DHFR has Ki values for antimicrobial antifolates pyrimethamine and trimethoprim which are significantly lower than the closely related T. cruzi or L. major DHFRs or than human DHFR.

Characterization of an unbalanced de novo rearrangement by microsatellite polymorphism typing and by fluorescent in situ hybridization

Unbalanced de novo rearrangements, difficult to characterize by conventional cytogenetic techniques, may be elucidated by molecular approaches. By dinucleotide repeat polymorphism typing and fluorescence in situ hybridization (FISH), we have defined the composition of an unbalanced de novo translocation (46,XX,15p+) in a child with multiple congenital anomalies. Use of a microsatellite repeat D5S208 (localized to 5p15) and polymerase chain reaction (PCR) analysis confirmed that the extra segment originated from the short arm of chromosome 5. Amplification of the patient's DNA with primers for dinucleotide repeats D5S350 and D5S118 showed that the entire 5p (from 5pter to 5q11) was present in 3 copies. FISH confirmed the trisomic status of 5p, and further revealed the presence of centromeres of both chromosomes 5 and 15 on the rearranged chromosome thus delineating its dicentric nature. This information allowed us to redefine the de novo rearrangement in this patient as 46,XX,dic der(15)t(5;15)(q11;p11).

[Compositive treatment of acute deep vein thrombosis of lower extremity]

Fourteen patients with acute deep vein thrombosis of lower extremity (DVT) were treated with composite methods including thrombectomy (iliofemoral venous thrombectomy and ascending venous thrombectomy), thrombolytic and anticoagulant therapy. Follow-up for 2-27 months (average 11.5 months) showed excellent and good results in 78.6%, and the morbidity of post-thrombotic syndrome only 21.4%. The remarkable results were due to opening of occlusive vein of the lower extremities by thrombectomy, which could make thrombolytics effective and reduce the dose of thrombolytics to prevent bleeding complication. Ascending venous thrombectomy could not only remove the venous thrombi of the lower extremities but also protect the deep venous valves and reduce the morbidity of postthrombotic syndrome. Additionally, to reach a satisfied therapy, lesion in iliac vein, such as anatomical compression, stenosis, occlusion, diaphragm and so on, shall be managed as well. Otherwise, DVT shall be recurrent.

Peak bone mass in young women

Increasing peak bone mineral density (BMD) or content (BMC) in young women may help to reduce the incidence of osteoporosis. Identifying the age when peak bone content or density is attained is essential to develop strategies aimed at optimizing peak BMD and BMC. Total body bone mineral density (TBBMD) and content (TBBMC) were measured by a dual X-ray absorptiometer in healthy females (n = 247, aged 11-32 years). TBBMD and TBBMC were modeled separately as a nonlinear function of age. By age 22.1 +/- 2.5 years, 99% of peak BMD is attained, and by age 26.2 +/- 3.7 years, 99% of peak BMC is attained. Nonlinear relationships between weight and TBBMD or TBBMC were also modeled. In this model, the influence of several parameters, including age, weight, and height, on BMC and BMD were simultaneously assessed. A model with age and weight described the best fit for TBBMD, whereas age, weight, and height described the best fit for total body TBBMC.

5-Fluoroindole resistance identifies tryptophan synthase beta subunit mutants in Arabidopsis thaliana

A study of the biochemical genetics of the Arabidopsis thaliana tryptophan synthase beta subunit was initiated by characterization of mutants resistant to the inhibitor 5-fluoroindole. Thirteen recessive mutations were recovered that are allelic to trp2-1, a mutation in the more highly expressed of duplicate tryptophan synthase beta subunit genes (TSB1). Ten of these mutations (trp2-2 through trp2-11) cause a tryptophan requirement (auxotrophs), whereas three (trp2-100 through trp2-102) remain tryptophan prototrophs. The mutations cause a variety of changes in tryptophan synthase beta expression. For example, two mutations (trp2-5 and trp2-8) cause dramatically reduced accumulation of TSB mRNA and immunologically detectable protein, whereas trp2-10 is associated with increased mRNA and protein. A correlation exists between the quantity of mutant beta and wild-type alpha subunit levels in the trp2 mutant plants, suggesting that the synthesis of these proteins is coordinated or that the quantity or structure of the beta subunit influences the stability of the alpha protein. The level of immunologically detectable anthranilate synthase alpha subunit protein is increased in the trp2 mutants, suggesting the possibility of regulation of anthranilate synthase levels in response to tryptophan limitation.

Cell individuality: a basic multicellular phenomenon and its role in the pathogenesis of disease

Every type of cell has its own special features that differentiate its members qualitatively from cells of other types. Within the same type of cells, however, every single cell also has its own unique characteristics that deviate itself from other individual cells, although they are alike collectively. These kinds of individual differences between cells are described here as cell individuality, which says basically that, within a cell population or even within a multicellular organism, every cell is a unique individual living being; and no single cell could be completely identical to another, regardless of how similar to each other they are. The individuality of a single cell can be represented by all sorts of cell characteristics, which are countless and range from physiological activities to molecular constituents. These individual differences in cell characteristics are generally presented much more in degree or in quantity, rather than in kind or in quality. Moreover, such cell individuality or quantitative variations within or even between cell populations may also play a basic role in the pathogenesis of disease, and particularly in the susceptibility of cells to the disease process.

Expression of Rb, E2F1, cdc2, and D, and B cyclins in developing spinal cord

The spatial and temporal distribution of transcripts for the tumor suppressor gene Rb, transcription factor E2F1, cdc2 kinase, cyclins D1, D2, B1 and B2 during neurogenesis of the spinal cord was determined by in situ hybridization. The Rb and E2F1 transcripts were detectable in proliferating and differentiating cells. By contrast, cdc2, cyclins D1, B1 and B2 are expressed in the ventricular zone where proliferating cells are localized. Cyclin D2 mRNA was detectable only in the marginal zone of the developing neural tube. Electrophoretic mobility shift analyses demonstrated a changing pattern of DNA/protein complexes that bind to E2F binding site. These observations suggest that Rb and E2F1 may be involved in the early stages of neuronal differentiation in addition to the cell cycle regulation.

Out-of-equilibrium CO2/HCO3- solutions and their use in characterizing a new K/HCO3 cotransporter

In typical physiological solutions, CO2 is in equilibrium with HCO3- and H+ (CO2 + H2O<==>HCO3- +H+). Because one cannot independently alter CO2 and HCO3- concentrations and pH, it is impossible to distinguish between the effects of CO2 and HCO3- on physiological processes. Here we describe a continuous-flow, rapid-mixing approach for generating out-of-equilibrium CO2/HCO3- solutions with a physiological pH and CO2 (but little HCO3-), or pH and HCO3- (but little CO2). We have exploited these out-of-equilibrium solutions to introduce HCO3- exclusively to either the outside or inside of a squid giant axon, and verify the presence of a new K/HCO3 cotransporter. The out-of-equilibrium approach could be useful in a variety of applications for independently controlling CO2 and HCO3- concentrations and pH.

On the nature of origins of DNA replication in eukaryotes

Chromosomal origins of DNA replication in higher eukaryotes differ significantly from those of E. coli (oriC) and the tumor virus, SV40 (ori sequence). Initiation events appear to occur throughout broad zones rather than at specific origin sequences. Analysis of four chromosomal origin regions reveals that they share common modular sequence elements. These include DNA unwinding elements, pyrimidine tracts that may serve as strong DNA polymerase-primase start sites, scaffold associated regions, transcriptional regulatory sequences, and, possibly, initiator protein binding sites and inherently destabilized regions. Based on the novel organization of chromosomal origin regions, we propose a model for initiation of DNA replication in higher eukaryotes. Unwinding of duplex DNA during initiation may be uncoupled, both temporally and spatially, from DNA synthesis, resulting in transient single-stranded intermediates that function in lieu of conventional replication forks during chromosomal DNA replication. DNA synthesis begins subsequently at multiple sites within the unwound regions rather than at specific origin sequences.