Decreased proteasome-mediated degradation in T cells from the elderly: A role in immune senescence

Induction of NFkappaB is a highly regulated process requiring phosphorylation, ubiquitination, and proteasome-mediated degradation of the cytosolic inhibitor IkappaBalpha. Analyses of the regulation of IkappaBalpha in TNF-alpha-treated T lymphocytes from young and elderly donors revealed severely compromised degradation of IkappaBalpha in T cells from the elderly. Examination of activation-induced phosphorylation and ubiquitination of IkappaBalpha did not demonstrate any significant age-related alterations. However, examination of proteasome activity in these T cells using fluorogenic peptide assays revealed a significant age-related decline in chymotryptic activity. These results suggest that a decline in proteasome activity results in a failure to fully degrade IkappaBalpha in the elderly. This failure to degrade IkappaBalpha may underlie both the observed decrease in NFkappaB induction and the IL-2 receptor expression in TNF-treated T cells during aging. Thus, decreased proteasome-mediated degradation may be central to immune dysfunction that accompanies aging.

Mammalian subtilisin/kexin isozyme SKI-1: A widely expressed proprotein convertase with a unique cleavage specificity and cellular localization

Using reverse transcriptase-PCR and degenerate oligonucleotides derived from the active-site residues of subtilisin/kexin-like serine proteinases, we have identified a highly conserved and phylogenetically ancestral human, rat, and mouse type I membrane-bound proteinase called subtilisin/kexin-isozyme-1 (SKI-1). Computer databank searches reveal that human SKI-1 was cloned previously but with no identified function. In situ hybridization demonstrates that SKI-1 mRNA is present in most tissues and cells. Cleavage specificity studies show that SKI-1 generates a 28-kDa product from the 32-kDa brain-derived neurotrophic factor precursor, cleaving at an RGLT downward arrowSL bond. In the endoplasmic reticulum of either LoVo or HK293 cells, proSKI-1 is processed into two membrane-bound forms of SKI-1 (120 and 106 kDa) differing by the nature of their N-glycosylation. Late along the secretory pathway some of the membrane-bound enzyme is shed into the medium as a 98-kDa form. Immunocytochemical analysis of stably transfected HK293 cells shows that SKI-1 is present in the Golgi apparatus and within small punctate structures reminiscent of endosomes. In vitro studies suggest that SKI-1 is a Ca2+-dependent serine proteinase exhibiting a wide pH optimum for cleavage of pro-brain-derived neurotrophic factor.

[Simultaneous determination of europium and copper in rare earth oxide by use AAS-PLS method]

Partial least squares regression was used to compensate for spectral "overlap" interference of Eu 324. 753 nm with Cu 324.754 nm in atomic absorption spectrometry. We could only use the copper element hollow-cathode lamp to simultaneous determine Eu and Cu in synthetic samples and rare earth oxide, and obtained satisfactory results.

Sensitivity of Drosophila heat shock transcription factor to low pH

The heat shock transcription factor (HSF) mediates the induction of heat shock gene expression. The activation of HSF involves heat shock-induced trimerization, binding to its cognate DNA sites, and the acquisition of transcriptional competence. In this study, the oligomeric properties of Drosophila HSF were analyzed by equilibrium analytical ultracentrifugation and gel filtration chromatography. Previous findings showed that trimerization of purified Drosophila HSF was directly sensitive to heat and oxidation (1). Here we report that low pH, in the physiological range, also directly induces HSF trimerization and DNA binding in vitro. Furthermore, the induction of HSF trimerization by low pH is synergistic with the actions of heat and oxidation. Since heat or chemical stress leads to a moderate decrease of intracellular pH, we suggest that intracellular acidification may contribute to activating the heat shock response in vivo.

Tubular-wire dual electrode for detection of thiols and disulfides by capillary electrophoresis/electrochemistry

A new dual-electrode detector for capillary electrophoresis is described. The detector consists of an integrated gold tubular electrode as the generator electrode and a gold wire electrode for detection. The detector configuration, including electrode size and position, has been optimized in terms of detection sensitivity and separation efficiency. After amalgamation of the dual electrode with mercury, the capillary electrophoresis/electrochemistry system was employed for simultaneous detection of thiols and disulfides. The response of cystine was found to be linear from 1 microM to 1 mM with a LOD of 0.5 microM (S/N = 3) and sensitivity of 60 pA/microM. The detection limits represent 200-fold improvement over previously reported dual-electrode designs for the detection of disulfides. The use of this detector for identification of thiol- and disulfide-containing peptides was demonstrated with a tryptic digest of ribonuclease A.

[Synthesis of adenine derivatives and their activities against herpes virus in vitro]

A series of 9-(N4-substituted acetaldehyde thiosemicarbazone) adenines were synthesized and evaluated for antiherpes virus activity. Compounds 4a-l were prepared by condensation of 9-(acetaldehyde) adenine(6) and the corresponding N4-substituted thiosemicarbazides (10). The antiviral effects of all compounds 4a-l were tested in vitro in primary rabbit kidney cell cultures infected with herpes simplex virus type 1 (HSV-1) and varicella-herpes zoster virus (VZV), and in primary human embryo cell cultures infected with herpes simplex virus type 2 (HSV-2). The results showed that the minimum inhibitory concentrations (MIC) of 4e and 4f for HSV-1 and VZV were 20, 40, 20 and 20 micrograms.ml-1, respectively, and other compounds were 200 micrograms.ml-1. For HSV-2, the MIC of all tested compounds were 300 micrograms.ml-1. We also evaluated the antiherpetic effect of 4e (and 4f) by combination with acyclovir (ACV) in the ratio of 1:1 in vitro. The MIC of the combined compounds were 2 micrograms.ml-1 for 4e and 6 micrograms.ml-1 for 4f, while their minimum cytotoxicities (MCC) in the cell were markedly reduced compared with the individual compounds.

[Effects of isorhapotigenin and resveratrol on function of peripheral blood polymorphonuclear leukocytes from rabbits]

In effects of isorhapotigenin and resveratrol on chemotaxis and release of beta-glucuronidase from rabbit peripheral blood polymorphonuclear leukocytes stimulated with formylmethionyl-leucyl-phenyl-phenylalanine (fMLPP) were studied. The optimal concentration of fMLPP for the induction of chemotaxis of polymorphonuclear leukocytes was approximately at 5 x 10(-10) mol.L-1. fMLPP, at the concentration range of 10(-10)-10(-6) mol.L-1, dose-dependently increased the release of beta-glucuronidase from polymorphonuclear leukocytes. Isorhapotigenin and resveratrol both inhibited the chemotaxis of polymorphonuclear leukocytes stimulated with fMLPP(5 x 10(-10) mol.L-1). Isorhapotigenin, at the concentration range of 10(-5)-10(-4) mol.L-1, dose-dependently inhibited the release of beta-glucuronidase from polymorphonuclear leukocytes stimulated with fMLPP(10(-8) mol.L-1). Resveratrol, at the concentrations of 1 x 10(-5) and 3 x 10(-5) mol.L-1, was shown to dose-dependently inhibit beta-glucuronidase release from polymorphonuclear leukocytes stimulated with fMLPP(10(-8) mol.L-1).

[A clinical observation on the leukopenia treated with shengbaikuai decoction]

OBJECTIVE

To study the effective orally taken medicine in treating the leukopenia.

METHODS

Ninety cases of leukopenia induced by chemotherapy were divided into 3 groups. They were test group treated with Shengbaikuai Decoction (SBK), control group and blank group. Their efficacies were compared with each other, 25 cases with nonchemotherapy were also observed.

RESULTS

WBC count and absolute neutrophil count (ANC) in test group were higher than those of other groups immediately after treatment and 2 weeks later (P < 0.01). The marked effective rate and total effective rate of test group after 2 weeks were 60.0% and 80.0% (P < 0.001) respectively, which were significantly higher than those of other groups. WBC and ANC count after treatment and 3 weeks later were higher than those before treatment in nonchemotherapy group (P < 0.001). The marked effective rate and total effective rate 3 weeks later were 64.0% and 80.0% respectively.

CONCLUSIONS

SBK could increase WBC count rapidly and definitely without apparent side effect.

Direct sensing of heat and oxidation by Drosophila heat shock transcription factor

The heat shock transcription factor HSF activates expression of its target genes in response to elevated temperatures and chemical or physiological stress. A key step in the activation process involves the formation of HSF homotrimers, leading to high-affinity DNA binding. The mechanism by which HSF trimerization and DNA binding is regulated by stress signals has remained elusive. Here, we report that trimerization and DNA binding of purified Drosophila HSF can be directly and reversibly induced in vitro by heat shock temperatures in the physiological range and by an oxidant, hydrogen peroxide. Other inducers of the heat shock response, including salicylate, dinitrophenol, ethanol, and arsenite, have no effect on HSF trimerization in vitro, indicating that these inducers act by indirect mechanisms.

[Effects of leukotrienes on production of interleukin 6 from mouse peritoneal macrophages]

In the present study, effects of leukotrienes on IL-6 production by mouse resident peritoneal macrophages were explored with a bioassay method involving IL-6 dependent murine hybridoma B9 cell line. The results showed that LTB4, LTC4 and LTD4 can enhance the production of IL-6 from cultured peritoneal macrophages of mice. The optimal concentractions for LTB4, LTC4 and LTD4 were found to be 1.45 x 10(-6), 6.9 x 10(-8) and 8.05 x 10(-8) mol.L-1, respectively. The results suggest that peptide leukotrienes might play important role on IL-6 production in the local milieu of inflammation.

[Simultaneous determination of cobalt and indium by atomic absorption spectrometry]

Present paper describes method which uses solution of simultaneous equations to compensate for spectral "overlap" interference of In 252.137nm with Co 252.136nm. Experimental results show that solution of simultaneous equations is possible method for resolving spectral interference in atomic absorption spectrometry. This method has been applied to determination of Co and In in the samples. Satisfactory results are obtained.

[Production and secretion of interleukin 6 from stimulated peritoneal macrophages of the mouse]

In this paper, a bioassay method involving the interleukin 6 dependent murine hybridoma B9 cell line was used to detect the level of released and cell-associated interleukin 6 in resident peritoneal macrophages from the mouse. The phorbol ester, phorbol 12-myristate 13-acetate (PMA), the calcium ionophores A23187, the chemotactic peptide fMLP and lipopolysaccharide(LPS) were introduced in these experiments as stimulators. PMA, A23187 and fMLP were shown to induce a dose-dependent increase of both released and cell-associated interleukin 6, whereas, LPS caused increase of interleukin 6 activity in supernatants of cultured peritoneal macrophages of the mouse. The effects of PMA and A23187 suggested that the pathway of PKC and calcium is involved in the production and secretion of interleukin 6. The effects of fMLP and LPS provided evidence that they participated in the process of inflammation. The difference between LPS and the other three stimulators in cell-associated interleukin 6 activity might suggest a different mechanism of actions of generation of interleukin 6.

[Human rotavirus infection in perinatal transmission]

OBJECTIVE

To investigate the perinatal infection of human rotavirus (HRV) in pregnant women and the effect on their neonates.

METHODS

HRV was examined by RT-PCR in cervical secretion and feces of 250 pregnant women and fecal samples of their neonates on the third postpartum day.

RESULTS

In pregnant women the HRV prevalence was 26.0% in feces and 8.8% in cervical secration, respectively. The infection rate of the 250 neonates in the first three days after birth was 4.4%, 15.6% and 22.0%, respectively. The HRV infection rate in neonates of infected mothers was 52.31%.

CONCLUSION

The infected mothers may be an important source for HRV infection of neonates. HRV transmitted via the labor tract and intrahospital transmission were the main sources for the neonatal infection.

[Characteristic mass and atomization efficiency of graphite furnace atomic absorption spectrometry]

Measurements of peak height and peak area characteristic masses and atomization efficiency for 7 elements (Ag, Bi, Cd, Cr, Ga, Ge and In) have been studied. The m0(i)(exp) values are compared with theoretical data, m0(i)(cal), to assess the effect of temperature on the correction factor of theorization for characteristic mass value (alpha = m0(i)(cal) m0(i)(exp)), the peak height and the peak area atomization efficiencies (betap and betai). The peak area atomization efficiency (betai) was equal to the correction factor of theorization for characteristic mass value (alpha) times tauD/tauR value. The tauR was value experimentally measured of atomic residence time and the tauD value calculated from rD = l2/8D. The betai value of elements always are smaller than the alpha values because the tauD/tauR values is less than one for most elements in the operating conditions. Past of the analyte vapours is readsorbed by the heated tube wall at high temperature and reevaporation of the adsorbed analyte followed by diffusion account for the larger atomic residence time and it appeared that the tauR value was larger than the tauD in graphite furnace.

Identification of a flexible loop region (297-313) of urokinase-type plasminogen activator, which helps determine its catalytic activity

Pro-urokinase has a much higher intrinsic catalytic activity than other zymogens of the serine protease family. Lys300(c143) in an apparent "flexible loop" region (297-313) was previously shown to be an important determinant of this intrinsic catalytic activity. This was related to the loop allowing the positive charge of Lys300(c143) to transiently interact with Asp355(c194), thereby inducing an active conformation of the protease domain (Liu, J. N., Tang, W., Sun, Z., Kung, W., Pannell, R., Sarmientos, P., and Gurewich, V. (1996) Biochemistry 35, 14070-14076). To further test this hypothesis, the charge at position 300(c143) and the flexibility of the loop were altered using site-directed mutagenesis designed according to a computer model to affect the interaction between Lys300(c143) and Asp355(c194). When the charge at Lys300(c143) but not Lys313(c156) was reduced, a significant reduction in the intrinsic catalytic activity occurred. Similarly, when the flexibility (wobbliness) of the loop was enhanced reducing the size of side chain, the intrinsic catalytic activity was also reduced. By contrast, when the loop was made less flexible, the intrinsic catalytic activity was increased. These findings were consistent with the hypothesis. The effects of these mutations on two-chain activity were less and often discordant with the intrinsic catalytic activity, indicating that they can be modulated independently. This structure-function disparity can be exploited to create a more zymogenic pro-urokinase (lower intrinsic catalytic activity) with a high catalytic activity, as exemplified by two of the mutants. The changes in intrinsic catalytic activity and two-chain activity induced by the mutations were due to changes in kcat rather than Km. Some significant structure-function differences between pro-urokinase and its highly homologous counterpart, tissue plasminogen activator, were also found.

In vitro characterization of the novel proprotein convertase PC7

Biochemical and enzymatic characterization of the novel proprotein convertase rat PC7 (rPC7) was carried out using vaccinia virus recombinants overexpressed in mammalian BSC40 cells. Pro-PC7 is synthesized as a glycosylated zymogen (101 kDa) and processed into mature rPC7 (89 kDa) in the endoplasmic reticulum. No endogenously produced soluble forms of this membrane-anchored protein were detected. A deletion mutant (65 kDa), truncated well beyond the expected C-terminal boundary of the P-domain, produced soluble rPC7 in the culture medium. Enzymatic activity assays of rPC7 using fluorogenic peptidyl substrates indicated that the pH optimum, Ca2+ dependence, and cleavage specificity of this enzyme are largely similar to those of furin. However, with some substrates, cleavage specificity more closely resembled that of yeast kexin, suggesting differential processing of proprotein substrates by this novel convertase. We examined the rPC7- and human furin-mediated cleavage of synthetic peptides containing the processing sites of three proteins known to colocalize in situ with rPC7. Whereas both enzymes correctly processed the pro-parathyroid hormone tridecapeptide and the pro-PC4 heptadecapeptide, neither enzyme cleaved a pro-epidermal growth factor hexadecapeptide. Thus, this study establishes that rPC7 is an enzymatically functional subtilisin/kexin-like serine proteinase with a cleavage specificity resembling that of hfurin. In addition, we have demonstrated that rPC7 can correctly process peptide precursors that contain the processing sites of at least two potential physiological substrates.

[Determination of atomization efficiency in graphite furnace with V-boat]

Based on that the absorbance is proportional to the effective length of the absorbing layer of atoms, a simple foumula is derived by which the atomization efficiency. Two atomization efficiencies were calculated: beta1 and beta2, which gave the fraction of calculated the total number of analytical atoms that enter the analysis volume during each stage of atomization. It is based on two different calculated ways for the mean residence time of atoms, and the beta1 and beta2 values of Ga and Tl in furnace with V-boat in various atomization temperatures were determined. Influence of the loss process of atomic vapor on the atomization efficiency value was discussed.

gamma-Interferon-induced resistance to 1,25-(OH)2 D3 in human monocytes and macrophages: a mechanism for the hypercalcemia of various granulomatoses

The hypercalcemia of various granulomatoses is caused by endogenous 1,25-dihydroxyvitamin D [1,25-(OH)2D3] overproduction by disease-activated macrophages. The inability of 1,25(OH)2D3 to suppress its synthesis in macrophages contrasts with the tight control of its production in macrophage precursors, peripheral blood monocytes (PBM). We examined whether 1,25(OH)2D3 resistance develops as PBM differentiate to macrophages or with macrophage activation. Normal human pulmonary alveolar macrophages (PAM) are less sensitive to 1,25(OH)2D3 than PBM, despite similar vitamin D receptor content; however, both PBM and PAM respond to exogenous 1,25-(OH)2D3 by inhibiting 1,25(OH)2D3 synthesis and inducing 1,25(OH)2D3 degradation through enhancement of 24-hydroxylase mRNA levels and activity. The human monocytic cell line THP-1 mimics PAM in 1,25(OH)2D3 synthesis and sensitivity to exogenous 1,25(OH)2D3. We utilized THP-1 cells to examine the response to 1,25(OH)2D3 with macrophage activation. Activation of THP-1 cells with gamma-interferon (gamma-IFN) enhances 1,25(OH)2D3 synthesis 30-fold, blocks 1,25-(OH)2D3 suppression of its synthesis, and reduces by 42.2% 1,25-(OH)2D3 induction of its degradation. The antagonistic effects of gamma-IFN are not merely restricted to enzymatic activities. In THP-1 cells and in normal PBM, gamma-IFN inhibits 1,25-(OH)2D3 induction of 24-hydroxylase mRNA levels without reducing mRNA stability, suggesting gamma-IFN inhibition of 1,25(OH)2D3 transactivating function. These results explain 1,25(OH)2D3 overproduction in granulomatoses and demonstrate potent inhibition by gamma-IFN of 1,25(OH)2D3 action in immune cells.

State-imposed limits on Medicaid reimbursement for nursing facility care

OBJECTIVES

Nursing cost-center limits were examined, along with their effects on Medicaid.

METHODS

A national survey of Medicaid nursing facility reimbursement provided data on cost centers for nursing, administration, and capital, whether in specific, larger, or multiple cost centers.

RESULTS

Most states impose nursing and administration limits. Far fewer states impose capital limits, but only capital limits may be related to constraint of reimbursement rates.

CONCLUSIONS

Shifting toward limiting capital costs, or simply eliminating cost-center limits, might accommodate cost control while removing negative constraints on direct resident care.

[The expression of proliferating cell nuclear antigen and p53 protein in salivary gland tumours]

The expressions and distributions of PCNA and p53 protein were studied with anti-PCNA and anti-p53 protein MoAbs, using immunohistochemical staining method in salivary gland tumour. The relationship between PCNA and p53 protein was also studied. Results indicated: Malignant mixed tumour (MmT) had a higher proliferating index (PI) of PCNA. The PI could be used as one of adjuvant diagnostic criteria; and as an important parameter for grading mucoepidermoid carcinoma (MEC); The positive expression of p53 might be a good tumour marker for MmT; Tumour tissues with positive expression of p53 had been shown higher PI of PCNA, however there was no significance difference in our group; It remained to be studied later.

[Human parvovirus B19 infection in perinatal transmission and abnormal fetuses]

OBJECTIVE

To investigate the perinatal infection of human parvovirus B19 in pregnant women and their fetuses.

METHODS

350 sera of normal pregnant women and 9 sera of abnormal fetuses were investigated by polymerase chain reaction (PCR) to check the parvovirus B19 DNA.

RESULTS

The prevalence of parvovirus B19 DNA was 1.14% and 0.28% in the sera of normal pregnant women and umbilical cords, respectively. Parvovirus B19 DNA was detected in 6 sera of pregnant women and umbilical cords from 9 abnormal fetuses parvovirus DNA could be detected by in situ hybridization in the nuclei of immature hematopoetic cells within fetal brain or spleen whose PCR tests were positive.

CONCLUSION

The results suggest that parvovirus B19 infection do exist in pregnant women and their neonates as well as fetuses in our country. PCR and in situ hybridization could provide more sensitive, more accurate and specific methods for clinical pathologic diagnosis and epidemic investigation.

Thermodynamics of dT--dT base pair mismatching in linear DNA duplexes and three-arm DNA junctions

We have used a combination of magnetic-suspension densimetry and calorimetry to derive complete thermodynamic profiles, including volume changes, for the formation of linear DNA duplexes and three-arm branched DNA junctions, from their component strands, with and without dT-dT mismatches. The formation of each type of complex at 20 degrees C is accompanied by a favorable free energy, with a favorable enthalpy term partially compensated by an unfavorable entropy. Formation is associated also with net uptake of water molecules. Using the formation of the fully-paired linear duplex or three-arm junction as reference states, we can establish a thermodynamic cycle in which the contribution of the single-strand species cancels. From this cycle, we determine that substitution of dA for dT has a differential free energy of deltadeltaG degrees of +2.4 kcal mol(-1) for mismatched duplex and +2.0 kcal mol(-1) (on the average) for the mismatched junction. These unfavorable differential free energies result from an unfavorable enthalpy, partially compensated by a favorable entropy, and a negative deltadeltaV. The free energies in the two cases have signs opposed to those of deltadeltaV, a situation that implicates hydration changes in creating the mismatch. When the deltadeltaV terms are normalized by the total number of base pairs involved, the immobilization of structural water molecules (and/or substitution of electrostricted for hydrophobic water molecules) is about 7 times greater for junctions than duplexes. This is consistent with more extensive hydrophobic hydration of branched DNA structures than of duplexes.

[Reasons of failure in blocking mother-infant transmission of HBV by using vaccine and related strategies]

We have detected the serum marker of HBV of 32 mothers whose HBsAg present positive and their children whom were given Hepatitis B vaccine immunization throughout duration of their mothers' pregnancy, altogether making up 66 cases. In 3 of these 32 families, Hepatitis B vaccine failed to block transmission between mother and infant. Direct nucleotide sequence analysis of HBV were carried out in 7 HBsAg positive infected persons. To confirm the possibility of HBV transmission between mother and infant on molecular level, we used PCR technique and DNA sequencing method. The reasons of which HBV vaccine failed in blocking transmission were discussed at the point of views of virus variation. Besides, we make and emphasized discussion on how to tighten up the measurement of controlling the course of infection and protecting susceptible population.

Proteolytic mapping of heat shock transcription factor domains

Heat shock transcription factors (HSFs) of higher eukaryotes respond to physical and cellular stress signals by trimerizing, binding to a specific site on DNA, and transactivating genes encoding the heat shock proteins. In this work, limited proteolysis was used as a biochemical probe of the domain organization of Drosophila HSF. Both unshocked monomeric and heat-shocked trimeric HSF possess an internal protease-sensitive region located between the amino-terminal and carboxyl-terminal hydrophobic heatad repeats, suggesting that this is a less structured region compared to those defined for DNA-binding, trimerization, and transactivation. For a few cleavage sites, the heat-shocked form of HSF is more accessible to proteases than the unshocked form, providing an additional diagnostic marker for inducible changes in conformation or modification between the latent and activated forms of HSF.

Functional analysis of human PACE4-A and PACE4-C isoforms: identification of a new PACE4-CS isoform

There are seven known subtilisin/kexin-like proprotein convertases responsible for the processing of numerous precursors at either pairs or specific single basic residues. Three members, PACE4, PC4 and PC5, exhibit alternative splicing of their RNAs resulting in the generation of multiple isoforms differing in their C- or N-terminal segments. In this study we examined the biosynthesis, functional activity and cellular localization of two of these isoforms, namely the full length PACE4-A and the C-terminally truncated PACE4-C which lacks 11 amino acids at the end of its chaperone-like P-domain. We report the existence of a new isoform, termed PACE4-CS, which is a C-terminally shortened version of PACE4-C. Cellular expression results demonstrated that PACE4-A codes for a functional secretable enzyme capable of cleaving pro7B2 into 7B2. In contrast, PACE4-CS is not secreted since it remains in the endoplasmic reticulum as an inactive zymogen form, thereby emphasizing the importance of the integrity of the P-domain. Microsequencing of the intracellular PACE4-CS protein in two cell lines revealed that it is proPACE4-CS with an N-terminal trimming reminiscent of the action of a dipeptidylpeptidase recognizing the motifs X-Ala and X-Pro.

Renal calcitriol synthesis and serum phosphorus in response to dietary phosphorus restriction and anabolic agents

Calcitriol [1,25-(OH)2D3] synthesis by the renal 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-hydroxylase) is induced in rats on a low phosphorus diet, but not in the hypophysectomized (HPX) or diabetic rat. However, the normal response is restored by the administration of growth hormone (GH) or insulin-like growth factor-I (IGF-I), or insulin, respectively. To further characterize this in vivo phenomenon, the acute effects of GH, IGF-I, and insulin were studied in the HPX rat. In the HPX rat the low phosphorus diet alone did not significantly alter serum phosphorus or 1alpha-hydroxylase activity, but treatment with GH resulted in a marked decrease in serum phosphorus that was associated with a fivefold induction of enzyme activity. Time course studies showed that by 6 hours after GH administration, hepatic IGF-I mRNA had increased 10-fold while renal IGF-I mRNA had increased by only 52%. Between 6 and 12 hours, serum phosphorus decreased dramatically and 1alpha-hydroxylase activity increased twofold. Treatment of phosphorus-restricted HPX rats with IGF-I resulted in a decrease in serum phosphorus by 2 hours that preceded a fourfold increase in enzyme activity between 6 and 10 hours. Treatment of phosphorus-restricted HPX rats with insulin produced similar results. This is the first demonstration of hypophosphatemia preceding induction of the 1alpha-hydroxylase after administration of IGF-I or insulin to the HPX rat on a low phosphorus diet. Although these growth factors may have a direct effect on the 1alpha-hydroxylase, these data suggest that the influence of GH, IGF-I, and insulin on transcellular phosphorus flux may have an independent effect on enzyme activity. Furthermore, the much greater induction of hepatic compared with renal IGF-I mRNA in response to GH suggests that systemic, rather than the local, IGF-I may be required for induction of the 1alpha-hydroxylase. This effect may be mediated by either the insulin or the IGF-I receptor.

Expression of the renal 25-hydroxyvitamin D-24-hydroxylase gene: regulation by dietary phosphate

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] plays a key role in phosphate (Pi) homeostasis through its phosphatemic actions on intestine and bone. In turn, dietary Pi restriction increases serum 1,25(OH)2D3 by stimulating its production, but its effect on vitamin D catabolism is less clear. Here we have examined the effects of dietary Pi on the expression of the renal vitamin D-24-hydroxylase (24-OHase), the first enzyme in the catabolic pathway for vitamin D compounds. Rats fed a low Pi (0.02% P) diet showed a fivefold decrease in renal 24-OHase mRNA compared with rats fed a normal Pi (0.67% P) diet. 24-OHase mRNA and 24-OHase activity decreased within 24 h of Pi restriction, reached a minimum by 48 h, and remained low through 14 days. Decreased 24-OHase mRNA was observed with more moderate Pi restriction (0.2% P), but higher Pi (1.2% P) did not increase 24-OHase mRNA over the 0.8% P diet. 24-OHase mRNA correlated well with plasma Pi (r = 0.862, P < 0.001). In conclusion, renal 24-OHase expression is regulated by dietary phosphate at the mRNA level.

Phosphorus restriction prevents parathyroid gland growth. High phosphorus directly stimulates PTH secretion in vitro

Dietary phosphorus (P) restriction is known to ameliorate secondary hyperparathyroidism in renal failure patients. In early renal failure, this effect may be mediated by an increase in 1,25-(OH)2D3, whereas in advanced renal failure, P restriction can act independent of changes in 1,25-(OH)2D3 and serum ionized calcium (ICa). In this study, we examined the effects of dietary P on serum PTH, PTH mRNA, and parathyroid gland (PTG) hyperplasia in uremic rats. Normal and uremic rats were maintained on a low (0.2%) or high (0.8%) P diet for 2 mo. PTG weight and serum PTH were similar in both groups of normal rats and in uremic rats fed the 0.2% P diet. In contrast, there were significant increases in serum PTH (130 +/- 25 vs. 35 +/- 3.5 pg/ml, P < 0.01), PTG weight (1.80 +/- 0.13 vs. 0.88 +/- 0.06 microg/gram of body weight, P < 0.01), and PTG DNA (1.63 +/- 0.24 vs. 0.94 +/- 0.07 microg DNA/gland, P < 0.01) in the uremic rats fed the 0.8% P diet as compared with uremic rats fed the 0.2% P diet. Serum ICa and 1,25-(OH)2D3 were not altered over this range of dietary P, suggesting a direct effect of P on PTG function. We tested this possibility in organ cultures of rat PTGs. While PTH secretion was acutely (30 min) regulated by medium calcium, the effects of medium P were not evident until 3 h. During a 6-h incubation, PTH accumulation was significantly greater in the 2.8 mM P medium than in the 0.2 mM P medium (1,706 +/- 215 vs. 1,033 +/- 209 pg/microg DNA, P < 0.02); the medium ICa was 1.25 mM in both conditions. Medium P did not alter PTH mRNA in this system, but cycloheximide (10 microg/ml) abolished the effect of P on PTH secretion. Thus, the effect of P is posttranscriptional, affecting PTH at a translational or posttranslational step. Collectively, these in vivo and in vitro results demonstrate a direct action of P on PTG function that is independent of ICa and 1,25-(OH)2D3.

Evaluation of a polymerase chain reaction-based assay for diagnosis of Wuchereria bancrofti infection

To assess the utility of a polymerase chain reaction (PCR)-based method for diagnosis of Wuchereria bancrofti infection, blood, plasma, and paraffin-embedded tissue samples were tested using a PCR-based assay that detects a W. bancrofti-specific repetitive DNA sequence. The assay was positive in 100 microL of blood from 40 of 42 microfilaria-positive subjects, the 2 subjects with negative assays having microfilarial counts of 1. Samples from 127 uninfected subjects were PCR-negative. The assay was also positive in 7 of 10 daytime samples in regions where infection is nocturnally periodic; PCR amplification from paraffin-embedded sections established the diagnosis of W. bancrofti infection in another 2 cases. A microtiter ELISA plate-based method was developed for rapid evaluation of large numbers of samples. These results suggest that this PCR-based assay will be useful in diagnosis of W. bancrofti infection in a variety of clinical settings.

[Effect of IL-4 on biological regulation of tumor cell lines]

The effect of IL-4 on biological regulation of tumor cell lines was observed by using human recombinant interleukin-4. The observation included cell proliferation, differentiation, cell surface marker and cytokine secretion. The effect of IL-4 on cell proliferation of nine cell lines was different. It showed 4/9 inhibitory effect, 3/9 enhancing effect and 2/9 no effect. The inhibitory effect of IL-4 on U937 cell proliferation was correlated with cell differentiation. IL-4 enhanced the expression of cell surface markers (including MHC class I, MHC class II and TAA) of some cell lines. Furthermore, IL-4 inhibited the production of IL-2 by MLA144. The preliminary results indicate that the effect of IL-4 on biological regulation of tumor cell lines is benefitial for controlling tumor cell growth and enhancing tumor cell recognition by effector cells. However, the down regulation also could be exerted.

A polymerase chain reaction assay for detection of the parasite Wuchereria bancrofti in human blood samples

To identify Wuchereria bancrofti DNA sequences that could be used as the basis for a simple and rapid parasite detection assay, a genomic library of W. bancrofti was constructed and screened for highly repeated DNA. The repeat found with the highest copy number was 195 basepairs (bps) long, 77% AT, and 300 copies per haploid genome. This sequence was designated the Ssp I repeat because it has a unique recognition site for that restriction endonuclease in all or most of the repeat copies. The Ssp I repeat DNA family is dispersed, genus-specific, and exists in all of the different geographic isolates of W. bancrofti tested. Based on DNA sequence analysis of this repeat, we have developed an assay to detect very small quantities of W. bancrofti DNA using the polymerase chain reaction (PCR). With this PCR assay, the Ssp I repeat was detected in as little as 1 pg of w. bancrofti genomic DNA (about 1% of the DNA in one microfilaria) added to 100 microliters of human blood. The PCR assay also amplified Ssp I repeat DNA from geographic isolates of W. bancrofti from around the world but not from other species of filariae or from human or mosquito DNA. Microfilaria-positive human blood samples collected in Mauke, Cook Islands were shown to be Ssp I PCR-positive, while microfilaria-negative samples were PCR-negative. The specificity and sensitivity of the Ssp I PCR assay indicates that this approach has significant potential for improved screening of large human populations for active W. bancrofti infection.

[Identification of vertical transmission of hepatitis B virus from mother to children by direct sequencing a segment of surface gene of hepatitis B virus]

SUBJECTIVE

To explore the reason for the failure to interrupt vertical transmission of hepatitis B virus (HBV) from mother to children in Chinese subjects by vaccination.

METHODS

HBV nucleotide sequences isolated from three sets of mother/children pairs were analyzed. HBV DNA from the surface antigen region encoding the amino acids 101 to 160 of hepatitis B surface antigen (HBsAg) was amplified and sequenced from HBsAg positive mother and their children.

RESULTS

Nucleotide and deduced amino acid sequences were absolutely identical in the mother and children in family one and two respectively. However, there were five nucleotides different in family one's isolates compared with the family two's isolates. All of them were a subtype. In one child of family three, with coexisted HBsAg and anti-HBs, sequencing result revealed a point mutation which predicted a change from glycine to arginine at residue 145 in the second loop of the determinant. The mother and another child had a glycine at this position.

CONCLUSION

This study revealed the vertical transmission linkage of HBV between the mother and children in a molecular level, and also first described a codon 145 immune escape mutant in Chinese vaccinated children.

Rat calcium-sensing receptor is regulated by vitamin D but not by calcium

Parathyroid hormone (PTH) secretion is regulated by extracellular calcium acting through a cell surface calcium receptor (CaR). We have examined the potential regulation of the CaR in the parathyroid glands (PTG) and kidney by calcium and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Rats fed vitamin D-deficient (-D) diets containing 0.02, 0.4, or 2.0% Ca had a wide range of serum ionized Ca (2.5-5.2 mg/dl) and PTH (22-590 pg/ml) concentrations. PTG CaR mRNA did not vary significantly with ionized calcium or PTH, indicating that hypocalcemia and hyperparathyroidism may not alter CaR expression. However, PTG CaR mRNA was 40% lower in the -D rats than in age-matched rats fed a vitamin D-replete (+D) diet (P < 0.002). Repletion of -D rats with 1,25-(OH)2D3 produced a dose-dependent increase in PTG CaR mRNA. Treatment of +D rats with 100 ng of 1,25-(OH)2D3 increased CaR mRNA by 33% (P < 0.05) and 54% (P < 0.002) in the PTG and by 89% (P < 0.02) and 91% (P < 0.02) in the kidney in two independent experiments. PTG CaR peaked at 16 h (150% of control, P < 0.05) after 1,25-(OH)2D3 administration but returned to normal by 24 h. This upregulation of CaR expression by 1,25-(OH)2D3 may be involved in the suppressive effects of vitamin D compounds on PTH secretion.

Dual-electrode detection for capillary electrophoresis/electrochemistry

The extremely low sample volumes required for capillary electrophoresis and the high sensitivity and selectivity of electrochemical detection make capillary electrophoresis/electrochemistry (CEEC) a very useful method for bioanalysis. In this paper, two types of dual-electrode detectors for CEEC are described. The first employs a ring-disk microelectrode placed in a wall-jet configuration and is used for the selective detection of substances undergoing chemically reversible oxidations. Collection efficiencies obtained for catecholamines with this configuration were between 25 and 35%. The second electrode design consists of two adjacent carbon fibers embedded in an epoxy matrix and is analogous to the parallel dual-electrode configuration used in liquid chromatography/electrochemistry. This configuration can be used to confirm peak identity and purity by operating the electrodes at two different potentials. Alternatively, it is possible to perform simultaneous oxidative and reductive electrochemical detection.

[Direct genotyping and antenatal diagnosis of deletional alpha-thalassemia of the southeast Asian type by polymerase chain reaction technique]

OBJECTIVE

To study the gene of deletional alpha-thalassemia of the Southeast Asian type (SEA) and to perform the antenatal diagnosis.

METHODS

A new method of polymerase chain reaction technique using three primers bridging the breakpoints was carried out for carrier detection and antenatal diagnosis of deletional alpha-thalassemia of the Southeast Asian type. A DNA fragment of about 630bp in size was amplified in case of--SEA alleles, while a 224 bp fragment was amplified in samples without the deletion. Homozygotes, heterozygotes, and normal subjects could be clearly distinguished with the present method.

RESULTS

We used this method in the genotyping and antenatal diagnosis of 10 high risk pregnancies of alpha-thalassemia. 2 homozygotes, 4 heterozygotes, and 4 normal infants were found.

CONCLUSION

The present method is simple and rapid in detection of carriers and antenatal diagnosis of the alpha-thalassemia of southeast Asian type.

Microtubules mediate cellular 25-hydroxyvitamin D3 trafficking and the genomic response to 1,25-dihydroxyvitamin D3 in normal human monocytes

The genomic actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the intracellular vitamin D receptor (VDR). Although immunocytochemistry has shown that disruption of microtubular assembly prevents nuclear access of the sterol-VDR complex, the role of microtubules in the response to 1,25(OH)2D3 has not been studied in viable cells. Our studies examined this interaction in normal human monocytes. Monocytes convert 25(OH)D3 to 1,25(OH)2D3 and to 24-hydroxylated metabolites more polar than 1,25(OH)2D3. Microtubule disruption totally abolished the ability of exogenous 1,25(OH)2D3 to suppress its own synthesis and to induce 24-hydroxylase mRNA and activity, without affecting either total 1,25(OH)2D3 uptake or maximal 1,25(OH)2D3-VDR binding. Thus, intact microtubules are essential for 1,25(OH)2D3-dependent modulation of gene transcription. Interestingly, microtubule disruption also decreased monocyte 1,25(OH)2D3 synthesis, not by decreasing the Vmax of monocyte mitochondrial 1 alpha-hydroxylase but through an increase in the Km for 25(OH)2D3. We examined 25(OH)D3 transport. Microtubule disruption did not affect total cellular 25(OH)D3 uptake but reduced its intracellular trafficking to the mitochondria. Thus, microtubules participate in intracellular 25(OH)D3 transport, and their integrity determines normal 1,25(OH)2D3 synthesis.

Loss of calcium responsiveness in cultured bovine parathyroid cells is associated with decreased calcium receptor expression

Suppression of PTH secretion by extracellular calcium is mediated by a plasma membrane calcium receptor (CaR). However, primary cultures of bovine parathyroid cells are known to quickly lose their responsiveness to extracellular calcium. The present study was designed to determine if the loss of calcium responsiveness is due to changes in CaR expression. In primary monolayer cultures of parathyroid cells, calcium-mediated suppression of PTH was still evident after 24 hours in culture but was completely absent after 6 days. This was preceded by a 75% drop in CaR mRNA content within 24 hours. CaR mRNA levels remained low for the 6-day culture. Earlier time points, examined in parathyroid cell suspensions, showed a 70% drop in CaR mRNA by 4 hours after collagenase-dispersion of the glands and an 85% drop after 24 hours. The decreased expression of CaR mRNA was not influenced by altering medium serum, calcium, or 1,25-dihydroxyvitamin D3. Our results indicate that the loss of responsiveness of cultured parathyroid cells to calcium is due to decreased CaR mRNA and, presumably, CaR protein expression.

Population awareness and control of hypertension and hypercholesterolemia. The Atherosclerosis Risk in Communities study

BACKGROUND

A national program for hypertension detection and control was implemented in the 1970s, whereas a similar program for control of hypercholesterolemia has been implemented in recent years. We studied the levels of awareness, treatment, and control of these conditions in US population samples during a 3-year period (1987 to 1989).

METHODS

The levels of awareness, treatment (by medication), and adequate control of hypertension (systolic blood pressure, > or = 140 mm Hg; diastolic blood pressure, > or = 90 mm Hg; or antihypertensive medication) and hypercholesterolemia (serum cholesterol level, > or = 6.21 mmol/L [> or = 240 mg/dL], or lipid-lowering medication) were studied among participants in the baseline examination of the Atherosclerosis Risk in Communities Study, including 15,739 individuals aged 45 to 64 years.

RESULTS

Eighty-four percent of the hypertensive subjects and 42% of the hypercholesterolemic subjects were aware of their conditions. Overall, 50% of the hypertensive subjects and only 4% of the hypercholesterolemic subjects had their conditions both treated and controlled. Rates of hypertension prevalence, awareness, and control remained stable during the 3-year study period. Hypercholesterolemia prevalence decreased from 30% in 1987 to 25% in 1989; its awareness increased from 31% to 50% during the same period. Hypertensive women were more likely than hypertensive men to be aware and treated, whereas hypercholesterolemia awareness was higher in men than in women. Hypertension awareness was highest in black women, but black hypertensive subjects were less likely than whites to be treated and to have their hypertension controlled. Black hypercholesterolemic subjects were less likely to be either aware or treated.

CONCLUSIONS

After the recent implementation of the National Cholesterol Education Program, the levels of awareness, treatment, and control of hypercholesterolemia are improving at a high rate, although they are still substantially lower than those for hypertension. Further improvement is necessary, particularly among certain population groups, such as blacks.

The roles of calcium and 1,25-dihydroxyvitamin D3 in the regulation of vitamin D receptor expression by rat parathyroid glands

Expression of the vitamin D receptor (VDR) in the parathyroid glands is decreased in secondary hyperparathyroidism associated with chronic renal failure by undefined mechanisms. In the present study, we examined the effects of hyperparathyroidism and dietary calcium and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on the expression of VDR in rat parathyroid glands. Vitamin D-deficient rats were maintained on diets containing 0.02% Ca (-D, LCD), 0.4% Ca (-D, NCD), or 2.0% Ca (-D, HCD) for 6 weeks. Serum ionized Ca (ICa) in the rats on the three diets ranged from 2.5-5.2 mg/dl. Serum PTH ranged from 22-590 pg/ml and correlated inversely with ICa (r = -0.835; P < 0.001). Rats with the highest ICa had normal PTH values, suggesting that vitamin D deficiency per se does not lead to hyperparathyroidism. VDR messenger RNA (mRNA) levels in the parathyroid glands correlated positively with ICa (r = 0.845; P < 0.001) and negatively with PTH (r = -0.716; P < 0.001). VDR mRNA levels in the rats fed the -D, HCD were 6 times higher than those receiving -D, LCD and the same as those in rats fed a normal (Purina) diet. Thus, prevention of hyperparathyroidism with high dietary calcium prevented the drop in VDR expression. Treatment of the rats on all three diets with 0, 25, or 100 ng 1,25-(OH)2D3, ip, 48 and 12 h before death dose dependently increased ICa and decreased PTH, as expected, and also increased parathyroid gland VDR mRNA. This coordinate regulation of VDR mRNA by calcium and 1,25-(OH)2D3 was also observed in the kidney, but intestinal VDR mRNA was not stimulated by dietary calcium or 1,25-(OH)2D3. Analysis of covariance for parathyroid gland VDR mRNA and ICa for the three doses of 1,25-(OH)2D3 revealed no significant independent effect of 1,25-(OH)2D3 on VDR mRNA, suggesting that the up-regulation of VDR expression by 1,25-(OH)2D3 in the parathyroid glands may be mediated primarily by increasing serum calcium.

A method for probing the topography and interactions of proteins: footprinting of myoglobin

We describe a procedure for mapping residues on the surface of a protein molecule to its sequence, using a scheme that is analogous to nucleic acid footprinting. The protein is end labeled radioactively and subjected to limited proteolysis, and the products are analyzed by denaturing polyacrylamide gel electrophoresis and autoradiography. The method is tested with the heme protein myoglobin and applied to mapping the (unknown) surface of the molecule lacking the heme group: apomyoglobin. Sites of protein-protein interaction can be identified, as illustrated by footprinting the association between myoglobin and an anti-myoglobin monoclonal antibody.

[Myocardial damage after high tension electricity injury in rabbits]

The experiment was designed to study the condition of rabbit myocardium after 10,000-Volt high tension electricity injury by using light and electron microscopes. Early change in myocardium was detected and it took a dynamic development. Also, the enzymogram of myocardium was found to be altered parallel with the pathological alteration, apart from significant changes showed in electrocardiograms. The result of the study demonstrated that organic injury occurred in myocardium after high tension electricity injury.

Equilibrium analysis of ethidium binding to DNA containing base mismatches and branches

In the processes of DNA replication, recombination, and repair, duplex DNA can transiently form branched structures, such as Holliday junctions, as well as base pair mismatches and bulges. These stages have altered ligand and protein binding properties from normal double helical DNA. A variety of ligands have been reported to interact more tightly at branches and bulges than to normal duplex sites. The stoichiometry, structural basis, and thermodynamics of this effect have not been determined. We have investigated the binding of the intercalator, ethidium bromide, to several DNA constructs including base mismatches, bulges, and three- and four-arm branched structures, using chemical footprinting, titration calorimetry, and fluorescence lifetime measurements. Two classes of binding sites are detected in three- and four-arm junctions in our high ionic strength conditions: one class is characterized by a small number of ligands (2-4 per DNA), with high binding affinity (K > 10(5)), and the second by a larger number of sites (10-12 per DNA) with lower affinity (K approximately 10(4)). By use of appropriate control experiments, the former appear to be associated with sites at or near the branch point or mismatch, while the latter are consistent with binding to the normal duplex DNA region(s) of the molecule. Titration calorimetry indicates an enthalpy of -10 to -13 kcal/mol for binding of ethidium to a mismatch or three- and four-arm branch point. The tight binding class is associated with a fluorescence lifetime of 12-16 ns, distinct from that of free ethidium (ca. 2 ns) and the longer lifetime observed for ethidium intercalated in duplex DNA (22-26 ns).

Effects of unpaired bases on the conformation and stability of three-arm DNA junctions

Three-arm DNA junctions, in which three double helices intersect at a branch, have unique structure and reactivity of bases at and near the branch. Their solution conformation is asymmetric in the presence of Mg2+, while bases at the branch are sensitive to single-strand-specific agents. Following the surprising report that unpaired bases at the branch stabilize three-arm junctions, we have investigated the geometry and thermodynamics of three-arm junctions containing pendant T and A bases. The results are consistent with additional structure formation in junctions containing up to four pendant bases at the branch: relative to the tight junction, the thermal stability of junctions with two T's or A's at the branch increases; bases near the branch become less reactive to single-strand-reactive probes; and the enthalpy of formation is more negative. The interaction of ethidium observed at the branch in three-arm junctions is enhanced in junctions with unpaired bases at the branch. The geometry of three-arm junctions is perturbed by the presence of pendant bases, as seen by measuring the electrophoretic mobility of junctions to which long duplex arms are appended pairwise.

Mapping tRNA and 5S RNA tertiary structures by charge dependent Fe(II)-catalyzed cleavage

Chemical and enzymatic footprinting experiments have made it possible to identify protein binding sites in DNA and RNA, and to localize structural differences within nucleic acids to a resolution of a single base pair. We show here that by combining three reagents, Fe(II).EDTA2-, Fe(II).EDDA and Fe2+, differential maps of sites in RNA that vary in their local conformation and/or charge can be constructed. Comparison of profiles with respect to controls in the absence of a counterion such as Mg2+ allows analysis of sites responsive to tertiary structure. A single site that is labile to metals such as Pb2+ exists in tRNA(Phe) and a number of other tRNA's; this site is hyper-reactive to Fe(II), but not to the other probes. Scission induced by the neutral complex, Fe(II).EDDA, offers the most general measure of surface accessibility, since its distribution about the target molecule is insensitive to charge. Enhanced cleavage by Fe(II) relative to the other agents is detected at several adjacent sites in 5S RNA, consistent with conformational mobility. Protection at a series of positions in the arm formed by loops E and D with helix IV suggests further that at low temperature this arm interacts with loop A and helix I.

Effect of T-T base mismatches on three-arm DNA junctions

In contrast to four-arm immobile DNA junctions, three-arm DNA junctions have unique structural and dynamic properties consistent with lack of a single dominant conformation. The effect of T-T base mismatches at the branch in a three-arm model junction has been investigated using a combination of electrophoretic mobility measurements, chemical footprinting experiments, and thermodynamic studies. The results indicate that three-arm junctions are only slightly destabilized by a mismatch flanking the branch, relative to four-arm junctions. The effect of a mismatch varies with the sequence and position of the site of the mismatch. Since a three-arm junction with two mismatches flanking the branch is as stable as two junctions each with a single mismatch, the stability of three-arm junctions is not determined by stacking interactions at the branch in a simple way. The properties of three-arm junctions with one or two mismatches are consistent with a picture in which the conformation is the result of several substrates in which base pairs flanking the branch are transiently open, allowing bases to interact with the remaining duplexes.

Conformation and thermodynamics of DNA "necks". Models for three-arm branch formation in a duplex

The properties of three-arm DNA junctions differ from those of four-arm junctions in several respects. Most apparently, bases flanking the branch are reactive to single strand specific agents in three-arm junctions but not four-arm junctions. To determine the basis for this, we have designed and synthesized a series of complexes in which a short duplex, a neck, progressively extends from a parent 16-mer DNA duplex. These structure allow us to investigate how a three-arm branch forms, and how its properties change as the neck extends. Comparison of the properties of a nicked duplex with those of the neck structures using native gel electrophoresis with reporter arms attached reveals progressively greater geometrical perturbation of the complexes as the number of base-pairs in the neck increases. Footprinting by single-strand specific reagents indicates that the reactivity to single-strand reagents near the branch occurs when only a single pair is possible. The branch in each neck interacts tightly with ethidium, as does a nick in the same duplex. The thermodynamics of neck formation have been evaluated by calorimetry and from the concentration dependence of absorbance temperature profiles. Each neck complex is destabilized with respect to duplex DNA or a nicked duplex, and has a lower enthalpy of formation despite the increased number of base-pairs present. A model is proposed to account for these properties in which the bases in the pair adjacent to the duplex interact directly with the duplex, via transient insertion.