Structural basis for heterogeneous kinetics: reengineering the hairpin ribozyme

The RNA cleavage reaction catalyzed by the hairpin ribozyme shows biphasic kinetics, and chase experiments show that the slow phase of the reaction results from reversible substrate binding to an inactive conformational isomer. To investigate the structural basis for the heterogeneous kinetics, we have developed an enzymatic RNA modification method that selectively traps substrate bound to the inactive conformer and allows the two forms of the ribozyme-substrate complex to be separated and analyzed by using both physical and kinetic strategies. The inactive form of the complex was trapped by the addition of T4 RNA ligase to a cleavage reaction, resulting in covalent linkage of the 5' end of the substrate to the 3' end of the ribozyme and in selective and quantitative ablation of the slow kinetic phase of the reaction. This result indicates that the inactive form of the ribozyme-substrate complex can adopt a conformation in which helices 2 and 3 are coaxially stacked, whereas the active form does not have access to this conformation, because of a sharp bend at the helical junction that presumably is stabilized by inter-domain tertiary contacts required for catalytic activity. These results were used to improve the activity of the hairpin ribozyme by designing new interfaces between the two domains, one containing a non-nucleotidic orthobenzene linkage and the other replacing the two-way junction with a three-way junction. Each of these modified ribozymes preferentially adopts the active conformation and displays improved catalytic efficiency.     

Inactivation of mycobacteriophage D29 using ferrous ammonium sulphate as a tool for the detection of viable Mycobacterium smegmatis and M. tuberculosis

There is still an urgent requirement for more sensitive, cost-effective methods for detection and susceptibility testing of mycobacteria in clinical samples. We have been investigating a simple bacteriophage-based system which could be used for both purposes. As this depends upon the detection of phages which have successfully infected cells, a key step is the efficient removal or inactivation of phages remaining free in the culture medium. We demonstrate here the use of ferrous ammonium sulphate as an effective agent for the inactivation of mycobacteriophage D29 without impairing phage replication in previously infected host bacteria. Using this property, we report the detection of viable Mycobacterium smegmatis, M. bovis BCG and M. tuberculosis using simple low-cost technology. The method is highly sensitive, since it is able to detect 10 colony-forming units of M. smegmatis. It is also rapid, with the detection of M. tuberculosis in sputum specimens within 48 h.     

Structure of the human paralemmin gene (PALM), mapping to human chromosome 19p13.3 and mouse chromosome 10, and exclusion of coding mutations in grizzled, mocha, jittery, and hesitant mice

OBJECTIVES: To assess the correlation of total prostatic size and prostate transition zone dimensions with various measurements of the severity of bladder outlet obstruction secondary to benign prostatic hyperplasia. METHODS: Prostate-specific antigen, creatinine, American Urological Association symptom score, bother score, urinary history, uroflowmetry, and post-void residual urine volume determination was followed by measurement of the prostate gland and transition zone on transrectal ultrasound images in 136 men undergoing systematic prostate biopsies. Patients were divided into five groups based on past urinary tract treatment history and the presence of prostate cancer on the biopsies. The total prostate and transition zone dimensions, as well as calculated prostate and transition zone volumes, were compared by Pearson correlation with both the subjective and objective voiding parameters in each patient group. RESULTS: The transition zone dimensions correlated positively with American Urological Association symptom score, bother score, and post-void residual urine volume and correlated negatively with maximum and mean flow rates, particularly in patients with no history of prostate surgery, alpha-blocker administration, urinary infections, irritative voiding symptoms, or prostate cancer. CONCLUSIONS: Transrectal ultrasound measurements of transition zone dimensions correlate better than total prostatic dimensions or calculated prostatic or transition zone volumes with the severity of benign prostatic hyperplasia. Of these, the transverse transition zone dimension demonstrated the best correlation; however, this correlation is probably not adequate for clinical utility.     

下一代通信技术对广播电视业务发展的影响(上)

下一代通信技术的发展会给广播电视业务的发展带来新的契机和挑战.广播电视业务的发展应充分考虑"多播"这一特征,开展多种信息服务,良好的质量和内容将成为广播电视在竞争中的"杀手锏".开发"多功能一体"的智能终端是开展数字广播电视业务的必然趋势和要求.借鉴通信的业务模式,构筑下一代广播网络,主动联合通信网和互联网开展新业务,是广播电视业进一步发展的关键.本文将结合下一代通信技术和广播电视业务的关系,从业务、传输和接入等角度分别进行讨论.     

我国钛白粉厂家将面临同跨国公司在国内市场的竞争

我国钛白粉厂家将面临在国内市场直接同跨国公司的竞争。建议国内钛白粉厂家调整产业结构,加强技术创新,迎接新挑战。     

Inhibition of pink color development in cooked, uncured ground turkey through the binding of non-pink generating ligands to muscle pigments

The pink color defect in cooked, uncured turkey is a sporadic problem that can result in economic loss and consumer dissatisfaction. Fourteen ligands were tested in ground turkey samples for their ability to reduce pink color development in control samples and in the presence of 150 ppm sodium nitrite or 1.0% nicotinamide (pink color producing agents). The 14 ligands evaluated were: 3-amino pyridine (AP), 4-benzoylpyridine (BP), diethylenetriamine pentaacetic acid (DA), ethylenedinitrilo-tetraacetic acid disodium salt (EA), 2,3 dihydroxybenzoic acid (DB), 3-ethyl pyridine (EP), trans 1,2-diaminocyclohexane-N,N,N',N' tetraacetic acid monohydrate (HA), calcium reduced nonfat dried milk (NM), 2,3 phthalic acid (PA), 3-picoline (PC), pyrrole (PY), pyridazine (PZ), pyridinedicarboxcylic acid (YA), and pyrazinedicarboxcylic acid (ZA). All ligands were incorporated into ground turkey at 0.20 mg/g (meat weight basis) except for NM (30 mg/g). Color was evaluated using a reflectance spectrophotometer to measure pigment changes (nicotinamide hemochrome, nitrosohemochrome) and with a chroma meter to determine CIE L* a* b* values. Reduction in pink color development was apparent with the addition of the ligand alone and in the presence of sodium nitrite and especially nicotinamide. The four most effective ligands tested were DA, EA, HA, and NM. In general, pink color reduction was highest in the ligand only and the ligand plus nicotinamide samples as was observed by CIE a* and nicotinamide hemochrome value reductions.     

A 5-year evaluation of ceramic inlays (CEREC)

BACKGROUND: The aim of this study was to evaluate the morbidity and mortality attributable to smoking. MATERIAL AND METHODS: A transversal study was performed in a reference population of residents of the province of Granada (Spain). The number of deaths in 1985, the number of patients admitted to public hospitals in 1987 and a sample of out patients in 1989 were gathered from the National Institute of Statistics and hospital registries, and a prospective collection from out patient clinics was also carried out. The diseases studied included: oropharyngeal, esophageal, pancreatic, laryngeal, lung, bladder and kidney carcinomas, ischemic cardiopathy, cerebrovascular stroke, peripheral arteriopathy and chronic obstructive lung disease (COPD). Statistical analysis was performed by populational etiologic fraction and the chi square test. RESULTS: Four point five percent of the total number of annual hospital admissions, 6.3% of the out patients, 15.9% of the mortality and 12.0% of the total number of potential years of life lost (TPYLL) were estimated to be attributable to smoking in individuals over the age of 15 years in the province of Granada. The most frequent causes of morbidity attributable to smoking were COPD and ischemic cardiopathy, and with regards to mortality, ischemic cardiopathy (28.5%), COPD (21.6%) and lung cancer (17.5%). Higher percentages were observed in males than in females and in the group from 46 to 65 years of age. CONCLUSIONS: Smoking is not only responsible for an important percentage of deaths, but also leads to premature death and a reduction in the quality of life which is translated into an excess of health care costs. Since the impact of smoking becomes particularly evident from 46 to 65 years of age, smoking prevention should be centered on the early years of life.