Downstream enhancer

NtrC-P dimerizes and binds to the enhancer sequence, where it appears to catalyze an ATP-depen-dent isomerization of the closed to open forms of the transcription initiation complex (Eq. 28-1).153/154 The isomerization may depend upon looping.152 Other operons that utilize the oN subunit of RNAP often also have upstream or downstream enhancers.155156... 

Cis elements involved in transcription in yeast (a) and in vertebrates (b). Upstream activator sequences (UAS) in yeast are similar in function to upstream enhancers in vertebrates. Yeast has no parallel to downstream enhancers found in vertebrates. 

The delivery of an increased Na+ load downstream enhances loss of K+ ions and protons at the level of the collecting tubules. 

The principal objective of technical service in the chemical industry is to provide timely and professional information and support to downstream customers regarding chemical products and thek uses. It is neither cost-effective nor necessary for a consumer of chemical products to develop a staff of speciahsts having detailed expertise in all aspects of chemical raw materials and thek uses, particularly in a time of increa singly complex and rapidly technologically driven economies. Rather, this variety of expertise is provided in the chemical marketplace by technical service professionals whose knowledge and skills are made available by chemical products suppHers. As such, successful chemical companies provide technical service as a critical element of thek offerings to the marketplace making use of this aspect of the value chain to enhance thek competitiveness. 

Bends and tee-pieces in pipework often create locally turbulent flow. This enhances the corrosivity of the process liquid. These effects should be minimized by the use of flow straighteners, swept tees and gentle bends. Flow-induced corrosion downstream of control valves, orifice plates, etc. is sometimes so serious that pipework requires lining with resistant material for some twelve pipe diameters beyond the valve. 

Where problems develop, there is always a cause-and-effect process. In this case, as oxygen infiltrates the CR system, enhanced condensate line corrosion results (i.e., corrosion over and above the level that may be caused by the carbonic acid formed during steam condensation). This enhanced corrosion, in turn, creates the potential for further downstream corrosion debris pickup by the returning condensate and transporting this material back to the FW system. 

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... 

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