The Regulation of Protein Biosynthesis

The de novo synthesis of proteins can be varied in response to external stimuli, such as hormones or heat stress. The regulation of protein biosynthesis ocems primarily via phosphorylation of translation initiation factors. The regulatory points in eucaryotes are, above all, the translation factors eIF-2 and elF-4. 

A well studied example for control at the level of eIF-2 is the regulation of protein biosynthesis in erythroid cells (review Chen and London, 1995). A decrease in the heme concentration in reticulocytes leads to inhibition of globin synthesis at the level... 

The protein kinase H RI (heme regulated eIF-2 kinase) was first identified in studies on the regulation of protein biosynthesis in erythroid cells. A decrease in the heme concentration in reticulocytes leads to inhibition of globin synthesis at the level of translation. This regulation mechanism ensures that only so much globin is produced as is heme available. If the level of heme drops, then HRI becomes activated. The activated HRI phosphorylates the eIF-2a subunit, which in turn shuts off protein biosynthesis (Fig. 1.48). The mechanism of regulation of HRI kinase by heme is not well understood. Heme binding sites have been identified on the N-terminus and the kinase domain of HRI. 

The use of a particular mature mRNA for protein biosynthesis is also highly regulated. The regulation can occur via the accessibility of the mRNA for the ribosome or via the initiation of protein biosynthesis on the ribosome. In this manner a given level of mature mRNA can specifically determine when and how much a protein is synthesized on the ribosome. 

R2R3 MYB and HLH transcription factors acting in concert (Table 3.1). More recently, proteins containing conserved WD40 repeats have been implicated in the regulation of flavonoid biosynthesis as well. Thus, it is by variations of the combination of MYB/HLH/WD factors that anthocyanin accumulation is controlled (Table 3.1). 

Furuya K. Hutchinson CR. The DnrN protein of Streptomyces peucetius, a pseudo-response regulator, is a DNA-binding protein involved in the regulation of daunorubicin biosynthesis. J Bacteriol 1996 178 631CU6318. 

S. typhimurium has 12 copies of this domain. That all 12 proteins with this domain are involved in the regulation of cellulose biosynthesis, but under different... 

Our work has focused on the regulation of PIP biosynthesis via PI 4-kinase. We have characterized two soluble activators of the plasma membrane PI 4-kinase (17,18). One of these, a soluble, 49-kDa protein (PIK-A49) has been purified and sequenced... 

As is developed in Chapter 5 (Regulation of Protein Biosynthesis), this theorem states that the continued synthesis and degradation of proteins and enzymes constitutes the life process by enabling the metabolic network to achieve negative entropy and remain in a far-from-equilibrium condition. 

As well as donating electrons to the MoFe protein, the Fe protein has at least two and possibly three other functions (see Section IV,C) It is involved in the biosynthesis of the iron molybdenum cofactor, FeMoco it is required for insertion of the FeMoco into the MoFe protein polypeptides and it has been implicated in the regulation of the biosynthesis of the alternative nitrogenases. 

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

Three regulators were identified by genetic analysis. The main repressor, KdgR, controls the transcription of pectinase genes, the intracellular catabolic pathway and the secretion machinery. The PecS repressor controls the production of pectate lyases and cellulases, the secretion machinery and the biosynthesis of a blue pigment. PecT acts as a repressor of the production of some pectate lyases. Other proteins are involved in the regulation of pectinase s5mthesis but their role is not well characterized. 

Stocco, D. M. 2001. StAR protein and the regulation of steroid hormone biosynthesis. Annu. Rev. Physiol., 63 193-213. 

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