GENE EXPRESSION AND PROTEIN SYNTHESIS

Protein Synthesis and Gene Expression. Development of the infection structures is accompanied by the synthesis of at least 15 differentiation-related (dr) proteins, i.e. proteins not present in the germling until differentiation is induced Fig. 4 (22. A downshift in the synthesis of some proteins also occurs during infection structure development. 

Kamme F. and Wieloch T. (1996) The effect of hypothermia on protein synthesis and the expression of immediate early genes following transientcerebral ischemia. Adv. Neurol. 71,199-206. 

It seems only reasonable to suppose that the ability of adenoviruses to induce cellular DNA synthesis and entry into the cell cycle in mammalian cells is of advantage to the virus replication cycle such a property could hardly have evolved for any other purpose. Bellett and colleagues (see, for example, Murray et al., 1982a) have pointed out the particular relevance of this ability to the natural conditions of infection. By contrast to the artificial laboratory situation in which the virus is usually provided with cells that are partially transformed (they are immortal) and undergoing rapid growth and division, most cells encountered by the virus in the natural host are likely to be arrested at the Gl/GO boundary. Thus, it would seem to be of considerable advantage to the virus to possess a mechanism that, soon after an adenovirus enters such a relatively inactive host cell, induces that cell to enter its most active biosynthetic state and, thus, provide maximal quantities of those cellular proteins upon which viral DNA synthesis and gene expression depend. 

Puromycin. Puromycin (19), elaborated by S. alboniger (1—4), inhibits protein synthesis by replacing aminoacyl-tRNA at the A-site of peptidyltransferase (48,49). Photosensitive analogues of (19) have been used to label the A-site proteins of peptidyltransferase and tRNA (30). Compound (19), and its carbocycHc analogue have been used to study the accumulation of glycoprotein-derived free sialooligosaccharides, accumulation of mRNA, methylase activity, enzyme transport, rat embryo development, the acceptor site of human placental 80S ribosomes, and gene expression in mammalian cells (51—60). 

Heat shock proteins (HSPs) are synthesized by cells in response to an increase in temperature, as well to various other stressful stimuli. Their main function is to ensure intracellular protein homeostasis, thus preserving the cells viability in the presence of aggression. Current evidence points to a protective role for HSPs in several aspects of critical disease, such as ischemia-reperfusion, ARDS, and multiple organ failure. The increase of a few degrees Celsius above the normal environmental temperature of cells leads to the heat shock response 1) rapid expression of heat shock genes, 2) suppression of normal protein synthesis, and 3) the ability of cells to survive a second and otherwise lethal heat challenge (thermotolerance). 

Poly(3HB) synthesis in various subcellular compartments could be used to study how plants adjust their metabolism and gene expression to accommodate the production of a new sink, and how carbon flux through one pathway can affect carbon flux through another. For example, one could study how modifying the flux of carbon to starch or lipid biosynthesis in the plastid affects the flux of carbon to acetyl-CoA and poly(3HB). Alternatively, one could study how plants adjust the activity of genes and proteins involved in isoprenoid and flavonoid biosynthesis to the creation of the poly(3HB) biosynthetic pathway in the cytoplasm, since these three pathways compete for the same building block, i. e., acetyl-CoA. 

The 20 common amino acids are required in large amounts for protein synthesis, and E. coli can synthesize all of them. The genes for the enzymes needed to synthesize a given amino acid are generally clustered in an operon and are expressed whenever existing supplies of that amino acid are inadequate for cellular requirements. When the amino acid is abundant, the biosyn-... 

The major metabolic, developmental and signal responsive pathways are determined by the functionality of proteins (notably enzymes) and the amounts of particular proteins. The turnover of proteins is determined by the dichotomy of gene expression (protein synthesis) and protein degradation. The nature and regulation of these various pathways are sketched below. 

---