DNA polymerase epsilon: the latest member in the family of mammalian DNA polymerases

DNA polymerase epsilon is a mammalian polymerase that has a tightly associated 3'----5' exonuclease activity. Because of this readily detectable exonuclease activity, the enzyme has been regarded as a form of DNA polymerase delta, an enzyme which, together with DNA polymerase alpha, is in all probability required for the replication of chromosomal DNA. Recently, it was discovered that DNA polymerase epsilon is both catalytically and structurally distinct from DNA polymerase delta. The most striking difference between the two DNA polymerases is that processive DNA synthesis by DNA polymerase delta is dependent on proliferating cell nuclear antigen (PCNA), a replication factor, while DNA polymerase epsilon is inherently processive. DNA polymerase epsilon is required at least for the repair synthesis of UV-damaged DNA. DNA polymerases are highly conserved in eukaryotic cells. Mammalian DNA polymerases alpha, delta and epsilon are counterparts of yeast DNA polymerases I, III and II, respectively. Like DNA polymerases I and III, DNA polymerase II is also essential for the viability of cells, which suggests that DNA polymerase II (and epsilon) may play a role in DNA replication.     

Vitamin E Status of Healthy Swedish Cattle*

Using high pressure liquid chromatography the serum concentration of vitamin E was measured in dairy cows fed either hay or silage as their main roughage, in calves fed milk-replacer, and in young intensively fed bulls. The concentrates fed to the cows, calves and bulls were supplemented with 5–10, 25 and 5–10 mg DL-α-tocopheryl acetate per kg, respectively, and the milk-replacer for the calves was supplemented with 50 mg DL-α-tooopheryl acetate per kg powder. Cows fed silage as their main roughage had higher serum vitamin E concentrations ( $${\rm{\bar x}}$$ : 3.8–5.2 mg/l) than cows fed only hay ( $${\rm{\bar x}}$$ : 2.5–4.1 mg/1). Lactating cows had higher vitamin E concentrations than dry cows ( $${\rm{\bar x}}$$ : 4.1–5.2 and 2.5–3.8 mg/l, respectively) and calves and bulls had much lower vitamin E concentrations ( $${\rm{\bar x}}$$ : 1.4 and 1.2 mg/l, respectively) than cows. Thirty per cent of the calves and 41 % of the bulls had serum vitamin E concentrations less than 1.0 mg/l, suggesting that in these animals the conventional level of supplementation of feeds with DL-α-tocopheryl acetate in Sweden is probably inadequate for the prevention of nutritional muscular degeneration and other negative effects.     

A human neuroblastoma cell line with a stable ornithine decarboxylase in vivo and in vitro

A human neuroblastoma cell line (Paju) grew in 10 mM difluoromethyl-ornithine, which at this concentration normally stops the growth of all mammalian cells. Ornithine decarboxylase from Paju was resistant to inhibition in vitro by difluoromethylornithine, and required 10 microM of the compound for 50% inhibition, whereas ornithine decarboxylase from SH-SY5Y cells (another human neuroblastoma) and from rat liver needed only 0.5 microM difluoromethylornithine. Paju ornithine decarboxylase also exhibited a long half-life (over eight hours) in vivo. The half-life of immunoreactive protein was significantly longer than that of the activity. The long half-life of ornithine decarboxylase in Paju cells leads to its accumulation to a specific activity of 2000 nmol/mg of protein per 30 min during rapid growth (the corresponding activity in SH-SY5Y cells was about 2.5). When partially purified ornithine decarboxylase from Paju cells was incubated with rat liver microsomes it was inactivated with a half-life of 75 min. This inactivation was accompanied by a fall in the amount of immunoreactive protein. In the same inactivating system partially purified SH-SY5Y ornithine decarboxylase had a half-life of 38 min and its half-life in vivo was 50 min. The corresponding values for rat liver ornithine decarboxylase were 45 min and 40 min, respectively. Rat liver microsomes also inactivated rat liver adenosylmethionine decarboxylase. These results suggest that Paju ornithine decarboxylase has an altered molecular conformation, rendering it resistant to (i) difluoromethylornithine and (ii) proteolytic degradation both in vivo and in vitro.     

Strain while skiing and hauling a sledge or carrying a backpack

Eight soldiers on skis transported three loads of different weights on the level, uphill and downhill. The load was placed either on a cargo sledge or in a backpack or divided between the sledge and the backpack. The sledge had a new type of haulage-shaft, which was fixed to both sides of the pelvis. A service belt spread the pull over the whole upper body. The physical stain of different transport methods and the serviceability of the sledge was studied by measuring heart rate (HR), oxygen consumption, ventilation, and perceived exertion. The results indicate that both absolute and relative strain were systematically lower when pulling the load on the sledge than when carrying it in the backpack and on the sledge. HR when pulling a load equal to the human body weight on the sledge was on average 133 beats X min-1; HR was significantly higher 144 beats X min-1 when the load was divided between backpack and sledge. At the lower load level the differences between the transport methods were not significant for HR, oxygen consumption or ventilation. Uphill travel increased oxygen consumption by about 50% over that on the level. Perceived exertion at all load levels was significantly lower with the sledge than with the backpack alone or in combination. The estimated maximal allowable working time emphasized the advantage of the sledge and the importance of high physical working capacity. The maneuverability of the sledge with the new haulage shaft was good and the braking mechanisms worked well.(ABSTRACT TRUNCATED AT 250 WORDS)     

Risk factors and 25 year risk of coronary heart disease in a male population with a high incidence of the disease: the Finnish cohorts of the seven countries study.

OBJECTIVE--To assess the efficacy of high serum cholesterol concentration, raised blood pressure, and smoking as predictors of coronary heart disease. DESIGN--Prospective cohort study of middle aged men conducted over 25 years. SETTING--Finish components of an ongoing international study (seven countries study). PARTICIPANTS--1520 Men who at age 40-59 in 1959 were free of clinically evident heart disease. INTERVENTIONS--At each follow up visit a detailed medical examination including resting electrocardiography was performed, blood pressure and serum total cholesterol concentration were measured, and smoking was assessed. MEASUREMENTS AND MAIN RESULTS--825 Deaths (54% of participants) occurred during follow up, of which 335 were due to coronary heart disease. The hazard ratio for death from coronary heart disease with respect to risk factors at entry were: for serum cholesterol concentrations above 8.4 mmol/l v below 5.2 mmol/l, 2.68 (95% confidence interval 1.62 to 4.42); for systolic blood pressure in the highest quintile v that in the lowest quintile, 2.46 (1.72 to 3.50); and for smoking 10 or more cigarettes daily v never smoking, 1.95 (1.36 to 2.79). The hazard ratios with respect to cholesterol concentrations and blood pressure remained constant during follow up but the ratio with respect to smoking diminished, mainly owing to men giving up the habit. The estimated conditional probability of a 50 year old man dying of coronary heart disease in the next 25 years ranged from 12% among those with the most favourable risk factor profile to 75% among those with the least favourable profile. CONCLUSIONS--High risk factor levels (as determined in this study) in middle aged men may greatly increase the absolute probability of death from coronary heart disease when the period of study is relevant to the human life span.     

Chloroplast DNA variation inAnemone s. lato (Ranunculaceae)

Chloroplast DNA of seven species belonging toAnemone (sectt.Omalocarpus, Anemonidium, andAnemonanthea),Hepatica, andPulsatilla have been analyzed by restriction enzymes. According to the dendrogram constructed, the sections ofAnemone and the generaHepatica andPulsatilla seem to be evolutionary approximately equidistant to each others. This supports the concept that these groups should be treated on a similar taxonomic level, either as genera or subgenera.     

Significance of Ca2+ and K+ in Micrasterias Growth and Morphogenesis

Significance of Ca²⁺ and K⁺ for the complex morphogenesis ofMicrasterias, which takes place through multipolar tip growth,was investigated. Studies with different external Ca²⁺ concentrationsand Ca²⁺ channel inhibitors LaCl₃ and verapamil indicate thatCa²⁺ and Ca²⁺ channels are essential in the development, whiletreatments with different K⁺ concentrations and K⁺ channel inhibitorTEA demonstrate that potassium or K⁺ channels are not neededin the process, albeit the existence of K⁺ channels. K⁺ is notneeded even for the regulation of turgor pressure, which wasfound to decrease clearly during cell development. The plasmamembrane ATPase inhibitors diethylstilbesterol (DES) and Na-orthovanadatestop morphogenesis and indicate the importance of ion pumpsin the developmental process. Both supraoptimal, external K⁺and Ca²⁺ cause abundant Ca²⁺ precipitate formation in chloroplasts,which shows that chloroplasts are important in regulation ofcytoplasmic Ca²⁺ metabolism and that K⁺ activates the uptakeof Ca²⁺ through Ca²⁺ channels. (Received June 13, 1995; Accepted September 13, 1996)     

Modelling crop growth and biomass partitioning to shoots and roots in relation to nitrogen and water availability,using a maximization principle

Many crop models relate the allocation of dry matter between shoots and roots exclusively to the crop development stage. Such models may not take into account the effects of changes in environment on allocation, unless the allocation parameters are altered. In this paper a crop model with a dynamic allocation parameter for dry matter between shoots and roots is described. The basis of the model is that a plant allocates dry matter such that its growth is maximized. Consequently, the demand and supply of carbon, nitrogen, and water is maintained in balance. This model supports the hypothesis that a functional equilibrium exists between shoots and roots.This paper explains the mathematical computation procedure of the crop model. Moreover, an analysis was made of the ability of a crop model to simulate plant dry matter production and allocation of dry matter between plant organs. The model was tested using data from a greenhouse experiment in which spring wheat (Triticum aestivum L.) was grown under different soil moisture and nitrogen (N) levels.Generally, the model simulations agreed well with data recorded for total plant dry matter. For validation data the coefficient of determination (r²) between simulated and measured shoot dry weight was 0.96. For the validation treatments r² was slightly lower, 0.94. In addition to dry matter production the model succeeded satisfactorily in simulating the dry weight of different plant organs. The response of simulated root to shoot ratio to the level of soil moisture was mainly in accordance with the measured data. In contrast, the simulated ratio seemed to be insensitive to the changes in the levels soil N concentration used in the experiment.The data used in the present study were not extensive, and more data are needed to validate the model. However, the results showed that the model responses to the changes in soil N and water level were realistic and mostly agreed with the data. Thus, we suggest that the model and the method employed to allocate dry matter between roots and shoots are useful when modelling the growth of crops under N and water limited conditions.     

The effects of continuous illumination on southern and northern Micrasterias strains

Different strains of Micrasterias (Chlorophyta, Conjugatophyceae); M. rotata (Grev.) Ralfs ex. Ralfs and M. denticulata Breb. ex. Ralfs var. angulosa (Hantzsch) W. & G. S. West from northern and southern Finland were treated with continuous illumination in order to study the cellular effects of the treatment and whether the tolerance to continuous light of the northern Finnish strains is related to the different daylenght conditions in northern and southern areas. During the growing season the Finnish strains normally live in long-day conditions or even in continuous light (between 60 and 70°N), and they also tolerated continuous illumination in the laboratory. Ultrastructural changes were found especially in the chloroplasts, where formation of calcium precipitates of different forms and sizes and also formation of plastoglobuli containing lipids appeared. However, even in 4-week treatments the ultrastructure of cells of these northern strains was not totally disrupted, contrary to what was found in southern M. torreyi , studied earlier. Southern and northern strains tolerated continuous illumination in different ways. They seem to differ from each other physiologically, and the differences are possibly located in their ionic metabolism and regulation. The injuries sustained during continuous illumination of Micrasterias may largely be caused by the accumulation of Ca²⁺ in cytoplasm and organelles, especially in the chloroplasts.     

Ribosomal RNA genes in Scots pine (Pinus sylvestris L.): Chromosomal organization and structure

The nuclear 18S, 5.8S and 25S rRNA genes exist as thousands of rDNA repeats in the Scots pine genome. The number and location of rDNA loci (nucleolus organizers, NORs) were studied by cytological methods, and a restriction map from the coding region of the Scots pine rDNA repeat was constructed using digoxigenin-labeled flax rDNA as a probe. Based on the maximum number of nucleoli and chromosomal secondary constrictions, Scots pine has at least eight NORs in its haploid genome. The size of the Scots pine rDNA repeat unit is approximately 27 kb, two- or threefold larger than the typical angiosperm rDNA unit, but similar in size to other characterized conifer rDNA repeats. The intergenic spacer region (IGS) of the rDNA repeat unit in Scots pine is longer than 20 kb, and the transcribed spacer regions surrounding the 5.8S gene (ITS1 and ITS2) span a region of 2.9 kb. Restriction analysis revealed that although the coding regions of rDNA repeats are homogeneous, heterogeneity exists in the intergenic spacer region between individuals, as well as among the rDNA repeats within individuals.