Assignment Example | Topics and Well Written Essays - 2250 words

Assignment Example The santa factor may bind to its specific receptor in the cytosol or on the nuclear membrane. This causes the formation of a receptor-ligand complex that then acts as an effector molecule on the DNA (transcription factor or co-factor). This is basically transcription regulation. Several pathways can be implicated. They include; acting as specificity factors, repressors, activators or enhancers. Taking that the santa-receptor complex acts as a repressor for gene transcription; this complex may bind to the operator portion of the DNA and prevent the DNA polymerase from transcribing a specific gene, or genes. In the given case, the gene coding for FuIL protein will not be transcribed. The result is that no mRNA is formed, and subsequently no synthesis of the protein. Alternatively, it may act as a post translational modifier. Here, it will modify the folding structure of the FuIL protein, and subsequently lead to the ‘exposure’ of the degron on the protein for action by ubi quitin conjugating enzymes E1, E2 and E3. Combinations of different ubiquitin-conjugating enzymes and other factors constitute other pathways of the ubiquitin system, each of which conjugates a specific subset of proteins. There is some evidence that certain sequence elements and structural motifs of target proteins are degradation signals which mark them for ubiquitination by a particular model of the ubiquitin system and for eventual degradation. When looking at the santa factor as a direct promoter of protein degradation, it may diffuse into the cell and bind to the FuIL protein (like an enzyme-substrate complex) causing a conformational change in its structure that exposes the normally hidden degron. As a ligand, it may also bind to a receptor that catalyzes the phosphorylation forming a phosphodegron which is specific to certain multiunit ubiquitin ligases. An example would be a serpentine receptor. The serpentine receptors are coupled to a plasma membrane phospholipase C that cleaves PIP2 to diacylglycerol and IP3. By opening calcium channels in the endoplasmic reticulum, IP3 raises cytosolic calcium. Diacylglycerol and calcium act to activate protein kinase C, which phosphorylates and changes the conformation of the protein. This may be exposure of the degron. This then leads to facilitated function of ubiquitin and proteasome complexes that target and destroy specific proteins. Polyubiquitin tagging of proteins (ubiquitin attachment site in proteins is commonly a lysine side chain) by specific enzymes (E1,2 and 3) provides the major source of selectivity in the process of degradation, whereas the 26S proteasome complex performs the protein unfolding necessary for cleavage of the ubiquitin tagged proteins. This also provides an avenue for selectivity for the FuIL, as the E3 may bind to the santa, become allosterically modified and thus become specific to the FuIL. Such a mechanism is evident where the growth-regulating plant indole auxin binds to a spec ific E3 ligase, and forms part of a protein-binding interface that allows high-affinity interaction with specific protein substrates. (Sharon M) ii) Santa Response Element. The santa response element acts as a secure site for binding of RNA polymerase and the required transcription factors such as the SREB. It thus acts as an operator for the operon in question. The SREB molecule requires transport into the nucleus so as to exert