Translational-repressor

Baez, M. V., and Boccaccio, G. L. (2005). Mammalian Smaug is a translational repressor that forms cytoplasmic foci similar to stress granules. J. Biol. Chem. 280, 43131—43140. 

Mader, S., Lee, H., Pause, A., and Sonenberg, N. (1995). The translation initiation factor eIF-4E binds to a common motif shared by the translation factor eIF-4gamma and the translational repressors 4E-binding proteins. Mol. Cell. Biol. 15, 4990-4997. 

The precise manner in which proteins with zinc fingers bind to DNA differs from one protein to the next. Some zinc fingers contain the amino acid residues that are important in sequence discrimination, whereas others appear to bind DNA nonspecifically (the amino acids required for specificity are located elsewhere in the protein). Zinc fingers can also function as RNA-binding motifs—for example, in certain proteins that bind eukaryotic mRNAs and act as translational repressors. We discuss this role later (Section 28.3). 

The r-protein operons are regulated primarily through a translational feedback mechanism. One r-protein encoded by each operon also functions as a translational repressor, which binds to the mRNA... 

Some proteins bind directly to mRNA and act as translational repressors, many of them binding at specific sites in the 3 untranslated region (3 UTR). So positioned, these proteins interact with other translation initiation factors bound to the mRNA or with the 40S ribosomal subunit to prevent translation initiation (Fig. 28-32 compare this with Fig. 27-22). 

FIGURE 28-37 Regulatory circuits of the anterior-posterior axis in a Drosophila egg. The bicoid and nanos mRNAs are localized near the anterior and posterior poles, respectively. The caudal, hunchback, and pumilio mRNAs are distributed throughout the egg cytoplasm. The gradients of Bicoid (Bed) and Nanos proteins lead to accumulation of Hunchback protein in the anterior and Caudal protein in the posterior of the egg. Because Pumilio protein requires Nanos protein for its activity as a translational repressor of hunchback, it functions only at the posterior end. 

Initiation (Figs. 29-10 and 29-11), elongation (Fig. 29-12), and termination are three distinct steps in the synthesis of a protein. A variety of specialized proteins are required for each stage of synthesis. Their sequential interaction with ribosomes can be viewed as a means of ensuring an orderly sequence of steps in the synthesis cycle. The rate of protein formation will depend upon the concentrations of amino acids, tRNAs, protein factors, numbers of ribosomes, and kinetic constants. The formation of specific proteins can also be inhibited by translational repressors, proteins that compete with ribosomes for binding to target mRNAs.287... 

The genes for the more than 50 kinds of ribosomal proteins are located in 20 or more operons. Despite this, their synthesis is strictly balanced. Control is exerted at the level of translation rather than transcription. At least one ribosomal protein encoded by a polycistronic operon acts as a translational repressor and acts when ribosomal protein synthesis exceeds that of ribosomal RNAs or when these proteins are not formed in equimolar quantities. 

As shown in the example of ferritin mRNA, the binding of the ribosome to the 5 end of the mRNA can be blocked by RNA-binding proteins at the same region. This case is an example of a negative regulation of translation by sequence-specific RNA-binding proteins. Such proteins are categorized as translation repressors (see Fig. 1.46). 

Dean, K.A., Aggarwal, A.K., Wharton, R.P. (2002) Translational repressors in DrosopAifct. Trends Genet. 18,... 

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