Ubiquitin-Mediated Processes in Erythroid Cell Maturation
The terminal differentiation of erythroblasts during erythrocyte maturation entails significant cellular remodeling. In avian cells this is accomplished in part by marked attenuation of nuclear transcription and in mammalian cells by the physical extrusion of the nucleus. Thus lacking the ability to replace all but those proteins required for maintenance of the mature erythrocyte, the normal complement of cellular constituents is subsequently modified by a highly active degradative mechanism(s) to yield a sub-population of proteins stable to such proteolysis. During this time many metabolic pathways are shunted by selective turnover of key enzymes. The enhanced degradation essential to erythroid cell maturation is assumed to involve the same ATP, ubiquitin-dependent multi-enzyme pathway responsible for cytosolic protein turnover within all eukaryotes. The mechanism(s) required to commit erythroblasts to enhanced degradation and to direct the resulting selective degradation of key enzymes provides a tractable model for the less acute regulation observed within nucleated cells. Characterization of the ATP, ubiquitin-dependent pathway in erythroid cells and recent observations in other cells and tissues subject to enhanced degradation in response to various experimental manipulations provides some understanding of the dynamics exhibited by this system during terminal differentiation.
KeywordsErythroid Cell Chicken Embryo Fibroblast Mature Erythrocyte Ubiquitin Activate Enzyme Ubiquitin Conjugate
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