Pathways and Controls of Epithelial Protein Synthesis

Studies of the biochemical pathways and controls involved in protein synthesis led initially to the description of a process occurring on polyribosomal complexes under the control of messenger RNA. Transfer RNA, aminoacyl-tRNA synthetases and an energy source were identified as components of the reactions which were predominantly localized to the cytoplasm of protein synthesizing cells. Recent investigations of general protein synthesis have focused upon the identification of the multiple factors involved in the initiation reaction, upon the mechanism of polypeptide chain elongation on ribosomes and upon the processes involved in termination of the synthetic steps. These data, as well as those concerned with ribosomal compartmentalization and subunit exchange, are reviewed in this communication.Specific studies of protein synthesis in epithelial systems (those derived from mammalian epidermis or hair root cells), indicate that the overall mechanism is similar to that in other eukaryotic systems. Synthesis occurs on the surface of ribosomes with additional requirements including transfer RNA and the aminoacyl-tRNA synthetases. Although the yield of polyribosomes from epithelial tissues is low because of high endogenous ribonuclease concentrations, evidence from several laboratories indicates that in vivo epithelial protein synthesis occurs on membrane and/or filament-bound polyribosomes.Enhanced protein synthesis has been documented in psoriasis vulgaris but neither the mechanism nor pathophysiologic significance of this abnormality has been defined