DNA replication in the hyperthermophilic archaeon Sulfolobus solfataricus

Studies of the DNA-replication machinery of Archaea have revealed striking similarities to that of eukaryotes. Indeed, it appears that in most cases Archaea possess a simplified version of the eukaryotic replication apparatus. Studies of Archaea are therefore shedding light on the fundamental processes of DNA replication in both domains of life.

Combined effects of red pepper and caffeine consumption on 24 h energy balance in subjects given free access to foods

The effects of red pepper and caffeine ingestion on energy and macronutrient balances were examined in eight Caucasian male subjects. All subjects participated in two randomly assigned conditions: control and experimental (red pepper and caffeine). After ingesting a standardized breakfast, subjects ate three meals ad libitum (lunch, dinner and breakfast) and snacks which were served approximately 2 h after the lunch and dinner over a 24 h period. Two appetizers with or without 3 g red pepper) were given before lunch and dinner, and a drink (decaffeinated coffee with or without 200 mg caffeine) was served at all meals and snacks except for the after-dinner snack. It is also important to note that on the experimental day, 8.6 and 7.2 g red pepper were also added to lunch and dinner respectively. Red pepper and caffeine consumption significantly reduced the cumulative ad libitum energy intake and increased energy expenditure. The mean difference in energy balance between both conditions was 4000 kJ/d. Moreover, the power spectral analysis of heart rate suggested that this effect of red pepper was associated with an increase in sympathetic:parasympathetic nervous system activity ratio. These results indicate that the consumption of red pepper and caffeine can induce a considerable change in energy balance when individuals are given free access to foods.

Bonding, structure, and energetics of gaseous E8(2+) and of solid E8(AsF6)2 (E = S, Se)

The attempt to prepare hitherto unknown homopolyatomic cations of sulfur by the reaction of elemental sulfur with blue S8(AsF6)2 in liquid SO2/SO2ClF, led to red (in transmitted light) crystals identified crystallographically as S8(AsF6)2. The X-ray structure of this salt was redetermined with improved resolution and corrected for librational motion: monoclinic, space group P2(1)/c (No. 14), Z = 8, a = 14.986(2) A, b = 13.396(2) A, c = 16.351(2) A, beta = 108.12(1) degrees. The gas phase structures of E8(2+) and neutral E8 (E = S, Se) were examined by ab initio methods (B3PW91, MPW1PW91) leading to delta fH theta[S8(2+), g] = 2151 kJ/mol and delta fH theta[Se8(2+), g] = 2071 kJ/mol. The observed solid state structures of S8(2+) and Se8(2+) with the unusually long transannular bonds of 2.8-2.9 A were reproduced computationally for the first time, and the E8(2+) dications were shown to be unstable toward all stoichiometrically possible dissociation products En+ and/or E4(2+) [n = 2-7, exothermic by 21-207 kJ/mol (E = S), 6-151 kJ/mol (E = Se)]. Lattice potential energies of the hexafluoroarsenate salts of the latter cations were estimated showing that S8(AsF6)2 [Se8(AsF6)2] is lattice stabilized in the solid state relative to the corresponding AsF6- salts of the stoichiometrically possible dissociation products by at least 116 [204] kJ/mol. The fluoride ion affinity of AsF5(g) was calculated to be 430.5 +/- 5.5 kJ/mol [average B3PW91 and MPW1PW91 with the 6-311 + G(3df) basis set]. The experimental and calculated FT-Raman spectra of E8(AsF6)2 are in good agreement and show the presence of a cross ring vibration with an experimental (calculated, scaled) stretching frequency of 282 (292) cm-1 for S8(2+) and 130 (133) cm-1 for Se8(2+). An atoms in molecules analysis (AIM) of E8(2+) (E = S, Se) gave eight bond critical points between ring atoms and a ninth transannular (E3-E7) bond critical point, as well as three ring and one cage critical points. The cage bonding was supported by a natural bond orbital (NBO) analysis which showed, in addition to the E8 sigma-bonded framework, weak pi bonding around the ring as well as numerous other weak interactions, the strongest of which is the weak transannular E3-E7 [2.86 A (S8(2+), 2.91 A (Se8(2+)] bond. The positive charge is delocalized over all atoms, decreasing the Coulombic repulsion between positively charged atoms relative to that in the less stable S8-like exo-exo E8(2+) isomer. The overall geometry was accounted for by the Wade-Mingos rules, further supporting the case for cage bonding. The bonding in Te8(2+) is similar, but with a stronger transannular E3-E7 (E = Te) bonding. The bonding in E8(2+) (E = S, Se, Te) can also be understood in terms of a sigma-bonded E8 framework with additional bonding and charge delocalization occurring by a combination of transannular n pi *-n pi * (n = 3, 4, 5), and np2-->n sigma * bonding. The classically bonded S8(2+) (Se8(2+) dication containing a short transannular S(+)-S+ (Se(+)-Se+) bond of 2.20 (2.57) A is 29 (6) kJ/mol higher in energy than the observed structure in which the positive charge is delocalized over all eight chalcogen atoms.

Preparation, X-ray crystal structure determination, lattice potential energy, and energetics of formation of the salt S4(AsF6)2.AsF3 containing the lattice-stabilized tetrasulfur [2+] cation. Implications for the understanding of the stability of M(4)2+ and M2+ (M = S, Se, and Te) crystalline salts

S4(AsF6)2.AsF3 was prepared by the reaction of sulfur with arsenic pentafluroide in liquid AsF3 (quantitatively) and in anhydrous HF in the presence of trace amounts of bromine. A single-crystal X-ray structure of the compound has been determined: monoclinic, space group P2(1)/c, Z = 4, a = 7.886(1) A, b = 9.261(2) A, c = 19.191(3) A, beta = 92.82(1) degrees, V = 1399.9(4) A3, T = 293 K, R1 = 0.052 for 1563 reflections (I > 2 sigma (I) 1580 total and 235 parameters). We report a term-by-term calculation of the lattice potential energy of this salt and also use our generalized equation, which estimates lattice energies to assist in probing the homopolyatomic cation thermochemistry in the solid and the gaseous states. We find S4(AsF6)2.AsF3 to be more stable (delta fH degree [S4(AsF6)2.AsF3,c] approximately -4050 +/- 105 kJ/mol) than either the unsolvated S4(AsF6)2 (delta fH degree [S4(AsF6)2,c] approximately -3104 +/- 117 kJ/mol) by 144 kJ/mol or two moles of S2AsF6 (c) and AsF3 (1) by 362 kJ/mol. The greater stability of the S(4)2+ salt arises because of the greater lattice potential energy of the 1:2 solvated salt (1734 kJ/mol) relative to twice that of the 1:1 salt (2 x 541 = 1082 kJ/mol). The relative lattice stabilization enthalpies of M(4)2+ ions relative to two M2+ ions (i.e., in M4(AsF6)2 (c) with respect to two M2AsF6 (c) (M = S, Se, and Te)) are found to be 218, 289, and 365 kJ/mol, respectively. Evaluation of the thermodynamic data implies that appropriate presently available anions are unlikely to stabilize M2+ in the solid phase. A revised value for delta fH degree [Se4(AsF6)2,c] = -3182 +/- 106 kJ/mol is proposed based on estimates of the lattice energy of Se4(AsF6)2 (c) and a previously calculated gasphase dimerization energy of 2Se2+ to Se(4)2+.

The function of DNA polymerase alpha at telomeric G tails is important for telomere homeostasis

Telomere length control is influenced by several factors, including telomerase, the components of telomeric chromatin structure, and the conventional replication machinery. Although known components of the replication machinery can influence telomere length equilibrium, little is known about why mutations in certain replication proteins cause dramatic telomere lengthening. To investigate the cause of telomere elongation in cdc17/pol1 (DNA polymerase alpha) mutants, we examined telomeric chromatin, as measured by its ability to repress transcription on telomere-proximal genes, and telomeric DNA end structures in pol1-17 mutants. pol1-17 mutants with elongated telomeres show a dramatic loss of the repression of telomere-proximal genes, or telomeric silencing. In addition, cdc17/pol1 mutants grown under telomere-elongating conditions exhibit significant increases in single-stranded character in telomeric DNA but not at internal sequences. The single strandedness is manifested as a terminal extension of the G-rich strand (G tails) that can occur independently of telomerase, suggesting that cdc17/pol1 mutants exhibit defects in telomeric lagging-strand synthesis. Interestingly, the loss of telomeric silencing and the increase in the sizes of the G tails at the telomeres temporally coincide and occur before any detectable telomere lengthening is observed. Moreover, the G tails observed in cdc17/pol1 mutants incubated at the semipermissive temperature appear only when the cells pass through S phase and are processed by the time cells reach G(1). These results suggest that lagging-strand synthesis is coordinated with telomerase-mediated telomere maintenance to ensure proper telomere length control.

The association between vigorous physical activities and fat deposition in male adolescents

PURPOSE

The aim of this study was to investigate the association between participation in vigorous physical activities (VPA) and indicators of adiposity and fat distribution in male adolescents.

METHODS

Subjects were classified on the basis of the number of reported 15-min periods over 3 d during which VPA were performed.

RESULTS

Body weight, fat mass, body mass index, sum of six subcutaneous skinfolds, trunk and extremity skinfolds, and trunk to extremity skinfolds ratio (T/E ratio) were all significantly and inversely related to a higher VPA participation. Moreover, T/E ratio was significantly lower in the subgroup reporting a mean of 7.8 15-min periods of activity for 3 d (equivalent to a mean of 39 min x d(-1)) compared with subjects reporting no participation. This decrease in T/E ratio was more pronounced in subjects reporting a mean of 13.6 15-min periods of VPA for 3 d.

CONCLUSION

These observations reinforce the idea that excess abdominal fat accumulation can be prevented by regular participation in vigorous physical activities.

Effects of red pepper on appetite and energy intake

Two studies were conducted to investigate the effects of red pepper (capsaicin) on feeding behaviour and energy intake. In the first study, the effects of dietary red pepper added to high-fat (HF) and high-carbohydrate (HC) meals on subsequent energy and macronutrient intakes were examined in thirteen Japanese female subjects. After the ingestion of a standardized dinner on the previous evening, the subjects ate an experimental breakfast (1883 kJ) of one of the following four types: (1) HF; (2) HF and red pepper (10 g); (3) HC; (4) HC and red pepper. Ad libitum energy and macronutrient intakes were measured at lunch-time. The HC breakfast significantly reduced the desire to eat and hunger after breakfast. The addition of red pepper to the HC breakfast also significantly decreased the desire to eat and hunger before lunch. Differences in diet composition at breakfast time did not affect energy and macronutrient intakes at lunch-time. However, the addition of red pepper to the breakfast significantly decreased protein and fat intakes at lunch-time. In Study 2, the effects of a red-pepper appetizer on subsequent energy and macronutrient intakes were examined in ten Caucasian male subjects. After ingesting a standardized breakfast, the subjects took an experimental appetizer (644 kJ) at lunch-time of one of the following two types: (1) mixed diet and appetizer; (2) mixed diet and red-pepper (6 g) appetizer. The addition of red pepper to the appetizer significantly reduced the cumulative ad libitum energy and carbohydrate intakes during the rest of the lunch and in the snack served several hours later. Moreover, the power spectral analysis of heart rate revealed that this effect of red pepper was associated with an increase in the ratio sympathetic: parasympathetic nervous system activity. These results indicate that the ingestion of red pepper decreases appetite and subsequent protein and fat intakes in Japanese females and energy intake in Caucasian males. Moreover, this effect might be related to an increase in sympathetic nervous system activity in Caucasian males.

Postexercise macronutrient oxidation: a factor dependent on postexercise macronutrient intake

BACKGROUND

It has been widely shown that exercise increases postexercise fat oxidation and energy expenditure.

OBJECTIVE

The aim of this study was to investigate the effect of exercise on postexercise substrate oxidation and energy expenditure when the exercise-induced expenditure of energy and macronutrients oxidized is compensated by an equivalent intake immediately after exercise.

DESIGN

Twenty-four-hour energy expenditure (24EE) and macronutrient oxidation of 8 young men were measured in a whole-body indirect calorimeter under the 2 following, randomly assigned conditions: 1) a control session of sedentary activities in the calorimeter for 61 h and 2) a similar session preceded by 60 min of exercise at 50% of maximal oxygen consumption. Immediately after exercising, subjects ingested a milk shake containing the same amount of energy (above resting metabolic rate) expended during exercise and with a food quotient corresponding to the mean exercise respiratory quotient. 24EE and substrate oxidation were compared between conditions on a day-to-day basis (days 1, 2, and 3) and for the 61-h observation period.

RESULTS

There was no difference in 24EE between the 2 conditions. Moreover, the composition of the postexercise fuel mix oxidized, as reflected by the respiratory quotient, was strictly the same under the 2 conditions.

CONCLUSION

Voluntary postexercise compensations in energy and macronutrient intakes play a major role in the ability of exercise to alter postexercise substrate utilization.

Cytological and functional aspects of telomere maintenance

The fact that eukaryotic chromosomes are linear poses a special problem for their maintenance: the natural ends of chromosomes must be distinguished from ends generated by chromosomal breakage and somehow, the chromosome ends must also be fully replicated to maintain their integrity. Telomeres, the complex structures at the ends of chromosomes are thought to be instrumental for both of these functions. However, recent insights in telomere biology suggest that these terminal structures do much more than just fulfill these two basic functions. Cytological data demonstrate that telomeres may play leading roles in chromatin organization and nuclear architecture during mitosis and meiosis. Moreover, non-functional telomeres may lead to genetic instability, a common prelude to cancer. Here, we review the basic functions of telomeres during chromosome replication and discuss the cytological aspects of telomere function during mitosis and meiosis.

Gender difference in the effect of body composition on energy metabolism

OBJECTIVE

The aim of this study was to investigate the relationship between energy expenditure (EE) and fat mass (FM) by using a cross-sectional approach to study the linear relationship between body composition variables and EE phenotypes as well as an intervention design to investigate the effect of body weight loss on energy metabolism in both genders.

METHODS

The correlations and linear relationships between body weight, FM, fat-free mass (FFM) and abdominal fat vs 24 h EE (EE 24) and sleeping metabolic rate (SMR) were compared between 65 men and 35 women, and before and after weight loss in 10 men and 10 women.

RESULTS

Our results showed that for a given FM, men displayed a higher EE than women, independently of FFM. Furthermore, regression analysis revealed that after body weight loss, men displayed a lower SMR for a given FM or FM adjusted for FFM compared to before the treatment, but this was not so in women. However, when FM was adjusted for abdominal fat deposition, the difference between the conditions was no longer observed.

CONCLUSIONS

FM has a significant impact on EE only in men. We suggest that abdominal adipose tissue may exert a potent regulatory effect on energy metabolism which would be more detectable in men who generally store more fat in this compartment than women.

Processing of telomeric DNA ends requires the passage of a replication fork

During telomere replication in yeast, chromosome ends acquire a long single-stranded extension of the strand making the 3' end. Previous work showed that these 3' tails are generated late in S-phase, when conventional replication is virtually complete. In addition, the extensions were also observed in cells that lacked telomerase. Therefore, a model was proposed that predicted an activity that recessed the 5' ends at yeast telomeres after conventional replication was complete. Here, we demonstrate that this processing activity is dependent on the passage of a replication fork through yeast telomeres. A non-replicating linear plasmid with telomeres at each end does not acquire single-stranded extensions, while an identical construct containing an origin of replication does. Thus, the processing activity could be associated with the enzymes at the replication fork itself, or the passage of the fork through the telomeric sequences allows a transient access for the activity to the telomeres. We therefore propose that there is a mechanistic link between the conventional replication machinery and telomere maintenance.

Acute effect of exercise and low-fat diet on energy balance in heavy men

OBJECTIVE

To quantify the acute effect of the exercise-low-fat diet combination on energy balance compared with sedentarity and a high fat diet in overweight individuals.

DESIGN AND MEASUREMENTS

We assessed the acute effect of exercise and ad libitum intake of low-fat foods on daily energy balance. Six heavy men participated in two randomly assigned sessions which required a 24 h stay in a whole body indirect calorimeter. Sessions were preceded by either a 60 min aerobic exercise at 50% VO2 max or a 60 min rest. Subjects were fed a low-fat diet (mean FO = 0.89) after exercise and a mixed diet (mean FQ = 0.85) after the resting period.

RESULTS

The difference in energy balance between the two conditions was 7.3 MJ. About half of the effect was attributable to the energy surplus expended during exercise whereas the remaining fraction was explained by the difference in post-exercise energy balance.

CONCLUSION

In heavy men, the combination of a low-fat diet and exercise has a strong acute effect on energy balance compared to a rest-mixed diet condition.

Cell cycle-regulated generation of single-stranded G-rich DNA in the absence of telomerase

Current models of telomere replication predict that due to the properties of the polymerases implicated in semiconservative replication of linear DNA, the two daughter molecules have one end that is blunt and one end with a short 3' overhang. Telomerase is thought to extend the short 3' overhang to produce long single-stranded overhangs. Recently, such overhangs, or TG1-3 tails, were shown to occur on both telomeres of replicated linear plasmids in yeast. Moreover, indirect evidence suggested that the TG1-3 tails also occurred in a yeast strain lacking telomerase. We report herein a novel in-gel hybridization technique to probe telomeres for single-stranded DNA. Using this method, it is shown directly that in yeast strains lacking the TLC1 gene encoding the yeast telomerase RNA, TG1-3 single-stranded DNA was generated on chromosomal and plasmid telomeres. The single-stranded DNA only appeared in S phase and was sensitive to digestion with a single-strand-specific exonuclease. These data demonstrate that during replication of telomeres, TG1-3 tails can be generated in a way that is independent of telomerase-mediated strand elongation. In wild-type strains, these TG1-3 tails could subsequently serve as substrates for telomerase and telomere binding proteins on all telomeres.