Other promoter elements

Possible mechanisms for enhancer action. (I) The enhancer draws the associated gene to the nuclear matrix, where it is more accessible to the transcription apparatus. (2) The enhancer is the initial binding site for an element that subsequently moves. (3) The enhancer folds or loops, depending on its polarity, to bind with other promoter elements. 

In a previous work [13], we reported on the preparation of carbon-supported bimetallic Bi-Pd catalysts by the thermal degradation of Bi and Pd acetate-type precursors under nitrogen at 773 K and described their catalytic properties in glucose oxidation. The formation of various BixPdy alloys (BiPd, BiPds, Bi2Pds) or, at least, associations on the surface of these catalysts during the activation step was heavily suspected. Alloy formation in supported bimetallic Pd-based catalysts has been mentioned several times in the literature in die presence of other promoting elements, like Pb or Te [14-16] and is sometimes assumed as responsible for the deactivation of the catalysts. 

A FIGURE 11-12 General pattern of control elements that regulate gene expression in multicellular eukaryotes and yeast, (a) Genes of multicellular organisms contain both promoter-proximal elements and enhancers, as well as a TATA box or other promoter element. The promoter elements position RNA polymerase II to initiate transcription at the start site and influence the rate of transcription. Enhancers may be either... 

Catalytic ammoxidation of alcohols was a direct outgrowth of groundbreaking propylene ammoxidation technology developed for acrylonitrile manufacture. Early disclosures by Distillers Co. Ltd. employed the same Sn-Sb-O-based catalysts found effective for the propylene ammoxidation reactions (93,94). Yields of HCN from methanol of up to 88% were obtained. Realization that the same families of metal oxide catalysts effective for the propylene aimnoxidation reaction could be used for methanol ammoxidation quickly led to a proliferation of patents that included Bi-Mo-0 (95-97) and Fe-Sb-0 (98). Researchers at Nitto Chemical Industry Co. Ltd. refined the Fe-Sb-0 propylene ammoxidation family of catalysts to optimize yields of HCN from methanol. They developed catalyst preparation methods to obtain an attrition-resistant version of the modified catalyst so that it could be operated in a fluid-bed reactor with all the concomitant economic and operating advantages that entails (99). The resulting Fe-Sb-O-based catalyst modified, with phosphorus in addition to the other promoter elements used... 

Catalysts that do not contain potassium lose activity very quickly because of coke deposition on the surface of the catalyst. Chemical changes that occur when the catalyst is removed from the operating environment make it very difficult to determine the nature of most of the promoter elements during the reaction, but potassium is always found to be present as potassium carbonate in the used catalyst. The other promoters are claimed to increase selectivity and the operating stabiUty of the catalyst. 

The DNA part of each control module can be divided into three main regions, the core or basal promoter elements, the promoter proximal elements and the distal enhancer elements (Figure 9.1). The best characterized core promoter element is the TATA box, a DNA sequence that is rich in A-T base pairs and located 25 base pairs upstream of the transcription start site. The TATA box is recognized by one of the basal transcription factors, the TATA box-binding protein, TBP, which is part of a multisubunit complex called TFIID. This complex in combination with RNA polymerase 11 and other basal transcription factors such as TFIIA and TFIIB form a preinitiation complex for transcription. 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

A third class of sequence elements can either increase or decrease the rate of transcription initiation of eukaryotic genes. These elements are called either enhancers or repressors (or silencers), depending on which effect they have. They have been found in a variety of locations both upstream and downstream of the transcription start site and even within the transcribed portions of some genes. In contrast to proximal and upstream promoter elements, enhancers and silencers can exert their effects when located hundreds or even thousands of bases away from transcription units located on the same chromosome. Surprisingly, enhancers and silencers can function in an orientation-independent fashion. Literally hundreds of these elements have been described. In some cases, the sequence requirements for binding are rigidly constrained in others, considerable sequence variation is... 

Within each species, individual promoters resulted in distinct, tissue-dependent accumulation patterns. The cauliflower mosaic virus (CaMV) 35S promoter, for example, led to high-level accumulation in callus and leaves whereas the maize ubiqui-tin-1 promoter was the best choice for producing recombinant proteins in cereal seeds even though it is not in itself seed-specific [23]. The lack of such comparative studies for proteins other than rAbs makes it difficult to generalize an optimal expression strategy for all proteins. Tables 7.1 and 7.2 list recombinant proteins expressed in plants and provide details of the production system, promoters and other regulatory elements used in each case. 

Figure 6 A general method for expressing prokaryotic tRNAs in mammalian cells, (a) A type-3 Pol III promoter, the H1 promoter, was combined with other gene elements in different ways to express the Escherichia coii amber suppressor tRNA . The GFP gene containing the TAG mutation at a permissive site serves as a fluorescence reporter for amber suppression. Translation of full-length GFP generates green fluorescence and indicates the expression of functional Escherichia coii amber suppressor tRNA in cells, (b) Total fluorescence intensity of cells transfected with constructs shown in (a). The combination in tRNA4 yields the most efficient tRNA expression.

The aim of this review paper is to give an extensive overview of the different promoters used to develop new or improved Co-based F-T catalysts. Special attention is directed towards a more fundamental understanding of the effect of the different promoter elements on the catalytically active Co particles. Due to the extensive open and patent literature, we have mainly included research publications of the last two decades in our review paper.In addition, we will limit ourselves to catalyst formulations composed of oxide supports, excluding the use of other interesting and promising support materials, such as, e.g., carbon nanofibers studied by the group of de Jong. ... 

On the other hand, the origin of the promoter metal and metal oxide effects is not always clear, despite the many detailed characterization studies. In what follows, we will give first a possible definition of the different promotion phenomena described in literature, as well as their mode of operation. The second part deals with an extensive literature overview of the effect of each promoter element on the F-T activity, selectivity and stability of the active Co phase. The different modes of operation will be evaluated for each element. Special attention will be paid to noble metal and transition metal oxide promotion effects. 

Noble Metal Promotion Effects. In the group of noble metals Ru, Re and Pt have been extensively studied as promoter elements for Co-based F-T catalysts, whereas other metals, such as Rh, Pd, Os and Ir, are only reported in limited occasions. Hence, we will focus our attention on the promotion effects induced by Ru, Re and Pt. 

A major goal in recombinant DNA technology is the production of useful foreign proteins by bacteria, yeast, or other cultured cells. Protein synthesis depends upon both transcription and translation of the cloned genes and may also involve secretion of proteins from the host cells. The first step, transcription, is controlled to a major extent by the structures of promoters and other control elements in the DNA (Chapter 28). Since eukaryotic promoters often function poorly in bacteria, it is customary to put the cloned gene under the control of a strong bacterial or viral X promoter. The latter include the X promoter PL (Fig. 28-8) and the lac (Fig. 28-2) and trp promoters of E. coli. These are all available in cloning vehicles. 

Induction of heat-shock proteins depends upon a heat-shock promoter element (HSE) that binds an activating transcription factor HSF.452-455 An increase in temperature not only induces synthesis of heat-shock proteins but represses synthesis of most other proteins. Thus, in E. coli or Salmonella a shift from 30°C to 42°C causes the appearance of 13 heat-shock proteins. At 50°C synthesis of almost all other proteins stops. In E. coli transcription of heat-shock genes is controlled by alternative factors, o32 and oE.456 456a... 

From the 1940s through the 1970s, while the MCS reaction was practiced industrially on a large scale, it was frequently the source of frustrating irreproducibility. The major treatises on the subject of Direct Process failed to mention the importance of promoter elements in the catalyst7-10. In addition, the use of substrates other than MeCl was explored only occasionally. Finally, there were few successful attempts to understand the Direct Process on a fundamental level before 1980. 

Observations that the 5 end of the mutation domain is near the transcriptional promoter stimulated speculation that the initiation of transcription is in some way involved in the generation of mutations. Betz et al. (1994) showed that the two transcriptional enhancer elements in the K locus, one in the JC intron and the other 9 kb 3 to CK, are important for effective hypermutation. The intron enhancer appeared to be absolutely required, whereas deletion of the 3 enhancer reduced but did not abolish mutation. The promoter 5 of the VK transcription start site (Falkner and Zachau, 1984 Parslow et al., 1984) was replaced by the human P-globin promoter without deleterious effect on mutation, indicating that specific promoter elements may not be required. Heavy chain transgenes with a heterologous promoter can also undergo mutation (Tumas-Brundage and Manser, 1997). 

Table 5.1 shows an application of XPS to the study of the promoted iron catalyst used in the Haber synthesis of ammonia. The sizes of the various electron intensity peaks allows a modest level of quantitative analysis. This catalyst is prepared by sintering an iron oxide, such as magnetite (Fe304) with small amounts of potassium nitrate, calcium carbonate, aluminium oxide and other trace elements at about 1900 K. The unreduced solid produced on cooling is a mixture of oxides. On exposure to the nitrogen-hydrogen reactant gas mixture in the Haber process, the catalyst is converted to its operative, reduced form containing metallic iron. As shown in Table 5.1, the elemental components of the catalyst exhibit surface enrichment or depletion, and the extent of this differs between unreduced and reduced forms. 

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