Initiation and regulation mechanisms of ribosomal RNA transcription in the eukaryote Acanthamoeba castellanii

Acanthamoeba rRNA transcription involves the binding of a transcription initiation factor (TIF) to the core promoter of rDNA to form the preinitiation complex. This complex is formed in the absence of RNA polymerase I, and persists for multiple rounds of initiation. Polymerase I next binds to form the initiation complex. This binding is DNA sequence-independent, and is directed by protein-protein contacts with TIF. DNA melting occurs in a separate step. In contrast to most prokaryotic transcription, melting occurs only following nucleotide addition and beta-gamma hydrolysis of ATP is not required as for polymerase II. Growth-dependent regulation of rRNA transcription is accomplished by modification of RNA polymerase I. The inactive form of polymerase (PolE) is unable to bind to the promoter and has altered heat stability. PolE is still active in elongation; thus, the modification affects the polymerase site involved in TIF contact. Modification of a polymerases I and III common subunit has been detected leading to the suggestion that transcription of stable RNAs of the ribosome might be co-regulated by this mechanism.

The statistical correlation of nucleotides in protein-coding DNA sequences

The statistical correlation of nucleotides in a DNA sequence is described by a set of redundancies D1, D2, D3, . . . . By calculation of [Dn] of 2341 coding regions of nucleic acid sequences it is demonstrated that about 2/3 of sequences has correlation length less than or equal to 2, 10% of sequences--correlation with 3-periodicity and others--long range aperiodic correlations. The implications of the results from the interactions of random mutation and natural selection are discussed briefly.

Differentiation of macrophage precursors to cells with LAK activity under the influence of CSF-1 and high dose IL-2

Mouse macrophage precursor cells with natural killer (NK) like activity, derived from in vitro culture of light-fraction-bone marrow cells in the presence of colony-stimulating factor 1 (CSF-1) and low dose IL-2, were incubated with high dose (1000 U/ml) IL-2. After 3 days of incubation, cells had developed from NK like (killing Yac-1 but not P815) into LAK-like (killing both YAC-1 and P815) effector cells. Morphological studies revealed that LAK activity occurred at the time when macrophage precursors with NK like activity containing few cytoplasmic granules had further differentiated into cells with abundant azurophilic granules in their cytoplasma. Proliferation of macrophage-precursor derived NK/LAK-like cells was dependent on the presence of colony-stimulating factor, generation of cytoplasmic granules was induced by IL-2 in a dose dependent way. Flow cytometric analysis showed that macrophage precursor-derived LAK effectors were positive for NK 1.1 but almost negative for F4/80. When the same starting cell population was cultured in the presence of 200 U/ml Interferon gamma (IFN gamma), proliferation was completely stopped and within 3-4 days all cells differentiated into mature macrophages expressing F4/80. In context with our previous data, we describe here a continuum of development from agranular macrophage precursors to granular cells with NK-like activity and further to cells with LAK activity under the influence of CSF-1 as growth factor and IL-2 as granule- and cytotoxicity-inducing factor.

A conserved sequence element in ribonuclease III processing signals is not required for accurate in vitro enzymatic cleavage

Ribonuclease III of Escherichia coli is prominently involved in the endoribonucleolytic processing of cell and viral-encoded RNAs. Towards the goal of defining the RNA sequence and structural elements that establish specific catalytic cleavage of RNase III processing signals, this report demonstrates that a 60 nucleotide RNA (R1.1 RNA) containing the bacteriophage T7 R1.1 RNase III processing signal, can be generated by in vitro enzymatic transcription of a synthetic deoxyoligonucleotide and accurately cleaved in vitro by RNase III. Several R1.1 RNA sequence variants were prepared to contain point mutations in the internal loop which, on the basis of a hypothetical 'dsRNA mimicry' structural model of RNase III processing signals, would be predicted to inhibit cleavage by disrupting essential tertiary RNA-RNA interactions. These R1.1 sequence variants are accurately and efficiently cleaved in vitro by RNase III, indicating that the dsRNA mimicry structure, if it does exist, is not important for substrate reactivity. Also, we tested the functional importance of the strongly conserved CUU/GAA base-pair sequence by constructing R1.1 sequence variants containing base-pair changes within this element. These R1.1 variants are accurately cleaved at rates comparable to wild-type R1.1 RNA, indicating the nonessentiality of this conserved sequence element in establishing in vitro processing reactivity and selectivity.

The N-methyl-D-aspartate antagonist, MK-801, fails to protect against neuronal damage caused by transient, severe forebrain ischemia in adult rats

The neuroprotective effects of dizocilipine maleate (MK-801), a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor/channel, were tested in the 4-vessel occlusion rat model of forebrain ischemia. Adult Wistar rats, treated intraperitoneally with MK-801 or saline using several different treatment paradigms were subjected to 5 (n = 208) or 15 (n = 62) min of severe, transient forebrain ischemia. In saline-treated animals, 15 min of ischemia (n = 13) produced extensive and consistent loss of pyramidal neurons in the CA1 zone of hippocampus. The degree and distribution of cell loss were not reduced by single dose preischemic administration of MK-801 at 1 (n = 7), 2.5 (n = 4), or 5 mg/kg (n = 8). In other animals subjected to 15 min of forebrain ischemia, multiple doses of MK-801 (5, 2.5, and 2.5 mg/kg) given immediately and at approximately 8 and 20 hr after cerebral reperfusion (n = 5) did not alter CA1 injury compared to saline-treated controls (n = 5). Five minutes of forebrain ischemia in saline-treated animals, (n = 82) resulted in significantly fewer (p less than 0.001) dead CA1 pyramidal cells and a greater variance compared to animals subjected to 15 min of ischemia. Power analysis of the preliminary saline-treated animals subjected to 5 min of ischemia (n = 22) indicated that 60 animals per group were necessary to detect a 15% difference between MK-801 and vehicle-treated groups. Multidose treatment with MK-801 (1 mg/kg) given 1 hr prior to 5 min of ischemia (n = 60) and again at approximately 8 and 16 hr after recirculation failed to attenuate hippocampal injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a methyl farnesoate binding protein in hemolymph from Libinia emarginata

Hemolymph from Libinia emarginata was tested for its ability to bind methyl farnesoate (MF), a JH-like compound found in many crustaceans. Hemolymph bound MF with moderate affinity (KD = 4.5 x 10(-6) M). Competitive binding studies showed that this binding was specific for MF, with farnesoic acid and JH homologues having less than 30 and 7%, respectively, of the relative binding activity of MF. JH acid and ecdysterone had no binding activity. MF binding activity was lost after pretreatment of hemolymph with heat or protease, suggesting that the binding component was a protein. Gel filtration analysis showed that the binding activity had a molecular weight of about 650,000.

Temperature dependence of plasmin-induced activation or inhibition of human platelets

It is known that at 37 degrees C plasmin may have two opposite effects on platelets: at high concentrations (greater than 1.5 caseinolytic units [CU]/mL), plasmin activates platelets; at lower concentrations (0.1 to 1.0 CU/mL) it inhibits platelet activation induced by thrombin, collagen, or calcium ionophore A23187. In this study, we report that when lowering the incubation temperature to 22 degrees C, plasmin at low concentrations (0.1 to 0.5 CU/mL) fully activated platelets. When platelets were treated with 0.2 CU/mL of plasmin, lowering the incubation temperature from 37 degrees C to 22 degrees C resulted in an increase in the expression of fibrinogen receptors, in platelet release and aggregation. Thromboxane A2 was not generated by plasmin treatment at either temperature. Ultrastructural studies showed that platelets responded to low-dose plasmin at 37 degrees C by forming pseudopods, centralizing granules without fibrinogen release, whereas at 22 degrees C the same dose of plasmin caused platelet degranulation with the appearance of alpha-granule fibrinogen within the lumen of the surface connected canalicular system. In addition, at 22 degrees C plasmin at doses insufficient to induce platelet aggregation potentiated platelet response to thrombin. Thus, we suggest that plasmin may initiate both activating and inhibitory processes within platelets and that the change of temperature could influence this balance. These results may be of clinical relevance, because the fibrinolytic system was found activated during cardiopulmonary bypass in which the temperature of patient's blood circulation was reduced. This temperature-dependent behavior is also an interesting model for a further study on platelet response to serine proteinases.

[Small-airway lesions induced by inhalation of asbestos dust in dogs--pathological and aetiological studies]

This paper presents the pathological changes of the small airways of dogs inhaling asbestos dust in the workshop of Xin Kong Asbestos Mine for 1 to 3 years. Dogs of the experimental group showed that variable degrees of dust deposition and fibrous tissue reaction were found in all the three types of the small airways-respiratory bronchioles, alveolar ducts and membranous bronchioles of both lungs. The lesions in the lung increased with the duration of exposure. These changes in the canine small airways resulting from asbestos dust were very much similar to those of the humans. In addition, deposited dust collected from the workshop of the asbestos mine, and 50 dust particles selected randomly in foci were identified in situ by energy dispersive X-ray analysis. Findings demonstrated that the majority of the dust particles in the foci was principally mixed silicate dust. Among them asbestos dust predominated absolutely, and there were more amphiboles than chrysotiles. Therefore, it is concluded that the small airway lesions induced in the dogs are mainly due to mixed asbestos dust, and that there appears to exist a dose-response relationship.

Circadian rhythms of body temperature and drinking and responses to thermal challenge in rats after PCPA

Body temperature (Tb) and drinking were measured for five days in male and female rats. On day 6 (S1) the rats were injected with saline. On day 7 (P1) they were injected with PCPA (300 mg/kg IP). Measurements continued for 12 days. Immediately after PCPA Tb dropped. After that, the amplitude of the daily Tb rhythm was significantly decreased from days P2-P5. Females were more affected than males. Nocturnality of drinking was decreased on days P2-P4. Because the peak of the Tb rhythm advanced after PCPA, while the peak of the drinking rhythm was delayed, we conclude that the attenuation of the Tb rhythm was a direct result of PCPA treatment rather than a masking effect due to the attenuation of other rhythms. Other rats were thermally challenged during the first week post-PCPA. There were no differences in ability to regulate Tb in the cold, and the small variations in the heat were overshadowed by gender differences.

Role of active center and lysine binding sites of plasmin in plasmin-induced platelet activation and disaggregation

Previous studies have shown that plasmin can activate platelets and can also disperse platelet aggregates by degradation of fibrinogen bound to platelets. In this study, the role of the active center and the lysine binding sites (LBS) of human plasmin in activating platelets and in dispersing platelet aggregates is investigated using aprotinin and the tripeptide Val-Phe-Lys-CH2Cl to inhibit the active center and using epsilon-aminocaproic acid (EACA) to specifically block the LBS. Our results show that the catalytic activity of plasmin is indispensable both for activating platelets and for dispersing platelet aggregates. Binding of plasmin to platelets through the LBS enhances its activating potential, since both EACA (1 mM) and Lys-plasminogen (molar ratio of plasminogen:plasmin at 2:1 to 4:1) inhibit plasmin-induced platelet activation, whereas Glu-plasminogen at a molar ratio of 15:1 had no effect. Furthermore, plasmin which lacks the LBS (miniplasmin), is about 3 fold less effective in activating platelets. However, plasmin binding through the LBS is not absolutely required to disperse platelet aggregates, since EACA at 30 mmol/l was unable to prevent disaggregation by plasmin (half disaggregation time: 40 min in the presence of EACA against 27 min in its absence). It also appeared that fibrinogen receptors on activated platelets are resistant to plasmin degradation, and that disaggregation of plasmin-induced platelet aggregates was much slower than the degradation of fibrinogen by plasmin.

Partial purification and characterization of a Ca(2+)-dependent protein kinase from pea nuclei

Almost all the Ca(2+)-dependent protein kinase activity in nuclei purified from etiolated pea (Pisum sativum, L.) plumules is present in a single enzyme that can be extracted from chromatin by 0.3 molar NaCl. This protein kinase can be further purified 80,000-fold by salt fractionation and high performance liquid chromatography, after which it has a high specific activity of about 100 picomoles per minute per microgram in the presence of Ca2+ and reaches half-maximal activation at about 3 x 10(-7) molar free Ca2+, without calmodulin. It is a monomer with a molecular weight near 90,000. It can efficiently use histone III-S, ribosomal S6 protein, and casein as artificial substrates, but it phosphorylates phosvitin only weakly. Its Ca(2+)-dependent kinase activity is half-maximally inhibited by 0.1 millimolar chlorpromazine, by 35 nanomolar K-252a and by 7 nanomolar staurosporine. It is insensitive to sphingosine, an inhibitor of protein kinase C, and to basic polypeptides that block other Ca(2+)-dependent protein kinases. It is not stimulated by exogenous phospholipids or fatty acids. In intact isolated pea nuclei it preferentially phosphorylates several chromatin-associated proteins, with the most phosphorylated protein band being near the same molecular weight (43,000) as a nuclear protein substrate whose phosphorylation has been reported to be stimulated by phytochrome in a calcium-dependent fashion.

[Determination of coumarins in radix Angelicae Dahuricae before and after processing]

This paper reports the contents of coumarins in Radix Angelicae Dahuricae before and after processing. By CS-930 TLC scanner, the total contents have been determined to be 0.190%, 0.571%, 0.178% and 0.421% respectively.

Low frequency of ras activation in 2-acetylaminofluorene- and 3'-methyl-4-(dimethylamino)azobenzene-induced rat hepatocellular carcinomas

Activation of ras protooncogenes in 11 2-acetylaminofluorene (AAF)-induced hepatocellular carcinomas (HCCs) or liver cell lines and 9 3'-methyl-(dimethylamino)azobenzene (3'-Me-DAB)-induced HCCs in rats was examined using the NIH3T3 cell transfection assay and oligonucleotide hybridization analysis. Only one cell line established from a AAF-treated rat liver demonstrated transforming activity with a point mutation and ATTA transversion at the second position of H-ras codon 61. The rates of ras activation were thus very low for both AAF- and 3'-Me-DAB-induced rat HCCs, the results thus extending and confirming the findings indicating that ras activation in rat HCCs induced by various type of carcinogens is infrequent.

In vitro progression-associated c-H-ras activation in neoplastic hepatocyte lines established from SV40-T antigen gene-harboring transgenic mice

In order to investigate the molecular mechanisms of multistep hepatocarcinogenesis in SV40-T antigen gene-harboring transgenic mice, 9 hepatocellular carcinoma (HCC) lines and 10 "preneoplastic" hepatocyte lines were established from the animals and their biological and molecular changes during culture were investigated. Three of the 9 HCC lines showed progression during culture in terms of growth rate and growth capability in soft agar and in nude mice. This progression was associated with the appearance of activated c-H-ras oncogene. Including these 3 lines, H-ras activation was observed in a total of 7 of the 9 HCC lines (78%), whereas it was found only in 1 of 10 (10%) "preneoplastic" hepatocyte lines. These data thus indicate that H-ras activation may be an event occurring at a relatively late stage of hepatocarcinogenesis in this transgenic mouse system and that it may serve towards completion of the carcinogenic process together with the T-antigen.

Absence of inhibition by lipoprotein (a) inhibition of tPA induced thrombolysis in a patient's plasma milieu

The increase in Lp(a) is strongly correlated with premature coronary artery disease. The Apo(a) has striking homology to plasminogen. It was found in an in vitro purified system that Lp(a) competes with both plasminogen and tissue-type plasminogen activator (tPA) for fibrin binding sites, thus resulting in a decrease in fibrin-dependent plasminogen activation. In this study, plasma fibrinolysis was studied in a young patient who had a consistently high level of Lp(a) (198 mg/dl) and had suffered from cerebral thrombophlebitis 12 months previously. The patient had normal levels of plasma plasminogen and fibrinogen. The euglobulin lysis time before and after venous occlusion was not prolonged, and after the addition of tPA to the patient's plasma or whole blood, the clot lysis time was normal. The same result was obtained when the patient's plasma was depleted of Lp(a) before clotting. When the patient's plasma serpins were inhibited, plasminogen activation by tPA in the presence of several fibrin concentrations was normal, suggesting that the formation of the ternary complex tPA - plasminogen - fibrin was not inhibited by the presence of high levels of Lp(a). It is concluded that a consistently high level of Lp(a) in this patient did not inhibit tPA-dependent fibrinolysis, and the thrombotic episode was not therefore related to deficient thrombolysis.