Translation initiation is a complex, multi-step process of fundamental importance in all kingdoms of life, during which the start site of the genetic message transmitted in the form of an RNA molecule (mRNA) is selected, and the level of translation determined. Being the slowest step of protein synthesis, initiation is the phase most often subject to regulation. Here we review, in a historical perspective and focusing mainly on results from our laboratory, the development of our perception of the mechanisms by which the most relevant steps of this pathway occur in bacteria. In particular, we describe: (a) the mechanistics and kinetics of translation initiation; (b) properties of mRNAs with and without Shine–Dalgarno sequence relevant for initiation site selection and translational efficiency; c) ribosomal binding and dissociation of the initiation factors, formation and properties of translation initiation intermediates; (d) the mechanisms by which translation initiation fidelity is ensured. Finally, we provide a short survey of the known translation initiation inhibitors. 相似文献
Three-axis orthogonal woven fabric composites composed of carbon fibres and epoxy resin have been fabricated. Examined from
micrographs, the fabric weaving yarns were found to be very slender with aspect ratios ranging from 11–13.6. Based upon the
observed geometry, the composite has been modelled by a unit cell comprising wavy yarns. Both elliptical and lenticular cross-sections
were adopted to simulate the slender weaving yarns. Taking into account one-dimensional stress concentration and yarn undulation,
an iso-phase approach has been developed to analyse the composite elastic moduli. A higher weaving yarn aspect ratio was found
to result in a lower modulus. Modulus reduction due to yarn undulation was more significant in weaving directions. Material
characterization has been conducted based upon monotonic tensile and three-point flexural tests, and detailed damage mechanisms
for both loadings have been examined. The onset of damage under tensile loading was found to be z-axis yarn debonding, followed
by debonding and splitting in y-axis yarns. When subjected to flexural loading, yarn debonding, transverse cracking, and interyarn
matrix cracking were the dominant damage mechanisms which appeared on specimen tensile sides. Stress transfer among yarns
and how it relates to the composite damage have been discussed in detail.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
Two types of samples were applied in this wire-bond evaluation work for an Al-pad diffusion process. One was finished product
for the cross-section examination of wire-bond and the other was without compound encapsulant used for the plane view examination
of wire-bond interface. These samples were aged at 175 C in air from 0 h to 1008 h. It is found that the normal product which
was ready on board existed ∼1 μm Au2Al and Au5Al2 phases. The Au2Al phase was then transformed to Au5Al2 phase in a 4 ∼ 72 h aging period. The Au4Al phase formed along with the Au5Al2 phase in 72 h to 240 h aging period showing some porosity within the reacted phases. The total phase thickness increased
to ∼4μm after 240 h aging. The Au4Al phase became the major phase after 336 aging h. The reacted phase layer thickness increased to ∼6 μm and reached the steady
state. A titanium-rich thin layer was also induced within the reacted phase layer. Three ternary phases as AlAu2Ti, AlAuTi, and Al2Au2Ti are found in this titanium-rich layer. In particular, Al2Au2Ti could be a new phase. 相似文献
The computational approach to the thermochemical changes involved in the process of explosion of a high energy materials (HEMs) vis-à-vis its molecular structure aids a HEMs chemist/engineers to predict the important thermodynamic parameters such as heat of explosion of the HEMs. Such a computer-aided design will be useful in predicting the performance of a given HEM as well as in conceiving futuristic high energy molecules that have significant potential in the field of explosives and propellants. The software code viz., LOTUSES developed by authors predicts various characteristics of HEMs such as explosion products including balanced explosion reactions, density of HEMs, velocity of detonation, CJ pressure, etc. The new computational approach described in this paper allows the prediction of heat of explosion (DeltaH(e)) without any experimental data for different HEMs, which are comparable with experimental results reported in literature. The new algorithm which does not require any complex input parameter is incorporated in LOTUSES (version 1.5) and the results are presented in this paper. The linear regression analysis of all data point yields the correlation coefficient R(2)=0.9721 with a linear equation y=0.9262x+101.45. The correlation coefficient value 0.9721 reveals that the computed values are in good agreement with experimental values and useful for rapid hazard assessment of energetic materials. 相似文献
When hydroquinone-O,Ooffiacetic acid is used as a linker arm in solid phase oligonucleotide synthesis, the time for NH4OH cleavage of oligodeoxy- or oligoribonucleotides is reduced to only 2 min. This allows increased productivity on automated DNA synthesizers without requiring any other modifications to existing reagents or synthesis and deprotection methods. The Q-linker may also be rapidly cleaved by milder reagents such as 5% NH4OH, potassium carbonate, anhydrous ammonia, t-butylamine or fluoride ion. However, the Q-linker is sufficiently stable for long-term storage at room temperature without degradation and no loss of material occurs during synthesis. The linker is also reasonably resistant to 20% piperidine/DMF, 0.5 M DBU/pyridine and 1:1 triethylamine/ethanol. The Q-linker can therefore serve as a general replacement for both succinyl and oxalyl linker arms. 相似文献
Fracture surfaces generated under combined bending–torsion fatigue loading in both the low-cycle fatigue and the high-cycle fatigue regions of specimens made of high-strength low-alloy Cr–Al–Mo steel are analysed in terms of topographical characteristics. Parameters reported here are the root mean square roughness, the number of peaks per unit length and the Hurst exponent quantifying various aspects of surface topography. As a main result of the analysis, the critical portion of torque beyond which the character of fracture topography significantly changes is estimated to be within the range of 40–50% of a total loading. 相似文献
XOR-based Visual Cryptography System (XVCS) is developed to achieve high contrast and good resolution of the recovered secret image. In general (k,n) VCS, the secret image can be visualized only if k or more than k shares are stacked together. In (k,n,t)? access structure, t number of participants are considered as the essential participants(t ≤ k ≤ n) whose shares are absolutely necessary to reconstruct the secret image. Several methods have been already proposed for the construction of (k,n)? VCS for black and white images. The major focus of this work is to design an XVCS for (k,n,t)? access structure for both black and white images and color images with maximum contrast. The experimental outcome shows that the proposed method has better results than other techniques proposed so far. Also, numerical examples are provided for (k,n,t)? XVCS for t =?1 and 2. The XVCS designed for (k,n,t)? access structure can be used for any real time application and is demonstrated with an example of user authentication in banking system.
This investigation utilized dynamic reblocking to enhance the RSA-based multisignatures scheme and solve the moduli clashes problem. In contrast to other RSA-based multisignature schemes, the proposed scheme has fewer modular exponentiations operations, overcomes the signing order problem, and minimizes the keys requirements. Consequently, the proposed scheme is suitable for application to all computer communication network environments 相似文献