Equilibrium and kinetic parameters of the sequence-specific interaction of Escherichia coli RNA polymerase with nontemplate strand oligodeoxyribonucleotides

The specific recognition by Escherichia coli RNA polymerase of single-stranded oligodeoxyribonucleotides (oligos) with the sequence of the -10 promoter region on the nontemplate strand has been studied. Binding was monitored by observing the increase in fluorescence of 2-aminopurine residues incorporated in the oligos. The effects of salt on the rates of formation and dissociation of RNA polymerase.oligo complexes are relatively small, from which we conclude that electrostatic interactions contribute minimally to the favorable binding free energy. From the convex temperature dependence of ln Ka (Ka is the equilibrium association constant), we infer that a large apparent negative heat capacity, of 1-2 kcal M-1 K-1, accompanies complex formation, which is interpreted as due to a conformational change in RNA polymerase. Contrary to expectation, the forward rate constant for binding of oligos is more than 10-fold smaller than that for open complex formation at strong promoters. This suggests that in comparison to an oligo, promoter DNA may be better able to accelerate this required conformational change in the RNA polymerase. Oligo binding was shown to compete with the interaction between RNA polymerase and promoters, indicating that the two bind to overlapping sites on the RNA polymerase     

Myosin conformational states determined by single fluorophore polarization

Muscle contraction is powered by the interaction of the molecular motor myosin with actin. With new techniques for single molecule manipulation and fluorescence detection, it is now possible to correlate, within the same molecule and in real time, conformational states and mechanical function of myosin. A spot-confocal microscope, capable of detecting single fluorophore polarization, was developed to measure orientational states in the smooth muscle myosin light chain domain during the process of motion generation. Fluorescently labeled turkey gizzard smooth muscle myosin was prepared by removal of endogenous regulatory light chain and re-addition of the light chain labeled at cysteine-108 with the 6-isomer of iodoacetamidotetramethylrhodamine (6-IATR). Single myosin molecule fluorescence polarization data, obtained in a motility assay, provide direct evidence that the myosin light chain domain adopts at least two orientational states during the cyclic interaction of myosin with actin, a randomly disordered state, most likely associated with myosin whereas weakly bound to actin, and an ordered state in which the light chain domain adopts a finite angular orientation whereas strongly bound after the powerstroke.     

Relationship between lead mining and blood lead levels in children

The authors studied blood lead levels of 226 randomly selected children, aged 6-92 mo, who lived in either a lead-mining area or a nonmining area, and 69 controls. The authors sought to determine to what extent mining activities contributed to blood lead levels in the children. The mean blood lead levels in the study and control groups were 6.52 microg/dl and 3.43 microg/dl, respectively. The corresponding proportions of children with elevated blood lead levels were 17% and 3%. Soil and dust lead levels were up to 10 times higher in the study than the control group. Elevated blood lead levels appeared to result from exposure to both lead-mining waste and lead-based paint. Mining waste was the cause of the higher prevalence of elevated blood lead levels in these children.     

Blind pleural biopsy using a Tru-cut needle in moderate to large pleural effusion--an experience

BACKGROUND: Pleural biopsy is invaluable for the etiological diagnosis of pleural diseases in the presence of an exudative pleural effusion. Conventionally, pleural biopsy is either performed with the Cope's or the Abrams pleural biopsy needles. A few investigators have used the Tru-cut biopsy needle with or without ultrasound guidance. We report our experience in performing closed pleural biopsy using a Tru-cut needle without ultrasound guidance in moderate to large exudative pleural effusion. We used a perpendicular approach to biopsy the pleura instead of the tangential approach described earlier. METHODS: Closed Tru-cut biopsy was performed in 27 consecutive patients with exudative pleural effusion who volunteered to undergo the procedure. The biopsy specimen was sent for histopathology. Pleural fluid analysis and other relevant investigations required to obtain a specific diagnosis were carried out. RESULTS: A specific diagnosis of tuberculosis was obtained on histopathology of pleural tissue in 12 out of 16 patients (diagnostic yield 75%) and in 5 out of 7 patients with malignancy (diagnostic yield 71%). Among the other 4 patients, other causes of exudative pleural effusion were detected in 3 and in 1 patient, no specific diagnosis could be made, despite extensive investigation. CONCLUSION: Closed pleural biopsy using a Tru-cut needle is effective for the specific diagnosis of exudative pleural effusion. The use of a perpendicular approach to biopsy the pleura does not seem to increase the complication in moderate to large pleural effusion.     

The thrifty-genotype hypothesis and its implications for the study of complex genetic disorders in man

The cases of eight Special Forces soldiers who sustained cold weather-related injuries while conducting winter training as part of Operation Arctic Saber in the Northwest Territories and Arctic Circle are reported. Environmentally related injuries can represent difficult diagnostic and treatment challenges in the field. Moreover, they may compromise the overall mission if they are not identified and treated early. Cold weather injuries can also result in long-term disfigurement and disability that may limit a soldier's future worldwide deployability. Mission requirements, equipment utilization, and environmental exposure place soldiers at particular risk for cold weather-related injuries in such austere settings. Nonetheless, with appropriate education and safety precautions, these potentially life-threatening risks can be greatly minimized.     

Primary leiomyosarcoma. A rare tumor of the adrenal gland

OBJECTIVE: To report on a rare case of primary leiomyosarcoma of the adrenal. To our knowledge, this is the fourth case reported in the literature. METHODS: A patient with primary leiomyosarcoma of the adrenal gland is presented. The clinical features are described, and the diagnostic and therapeutic aspects of this rare primary mesenchymal tumor are discussed. RESULTS/CONCLUSIONS: The aggressive nature and the poor prognosis of this rare tumor type are emphasized.