Effect of different leucine supplementation in low protein diet on Protein Synthesis and Activation of Translation Initiation Factors of Weaned Piglets

Both the process and synthesis of factors required for protein synthesis (or translation) account for a large proportion of cellular activity. In eukaryotes, the most complex and highly regulated phase of protein synthesis is that of initiation. For instance, across eukaryotes, at least 12 factors containing 22 or more proteins are involved, and there are several regulated steps. Recently, the localization of mRNA and factors involved in translation has received increased attention. The present review provides a general background to the subcellular localization of mRNA and translation initiation factors, and focuses on the potential functions of localized translation initiation factors. That is, as genuine sites for translation initiation, as repositories for factors and mRNA, and as sites of regulation.

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The regulation of protein synthesis in the liver of rats. Mechanisms of dietary amino acid control in the immature animal

Biochemical Journal ◽

10.1042/bj1070615 ◽

1968 ◽

Vol 107 (5) ◽

pp. 615-623 ◽

Cited By ~ 35

Author(s):

R. W. Wannemacher ◽

W. K. Cooper ◽

M. B. Yatvin

Keyword(s):

Amino Acids ◽

Protein Synthesis ◽

Amino Acid ◽

Specific Radioactivity ◽

Protein Diet ◽

Low Protein Diet ◽

Deficient Diet ◽

Low Protein ◽

Rna Content ◽

Cytoplasmic Rna

Weanling (23-day-old) rats were fed either on an amino acid-deficient diet (6% of casein, which in effect represents an ‘amino acid-deficient’ diet) or on a diet containing an adequate amount of protein (18% of casein) for 28 days. The hepatic cells from the animals fed on the low-protein diet were characterized by low amino acid content, almost complete inhibition of cell proliferation and a marked decrease in cell volume, protein content and concentration of cytoplasmic RNA compared with cells from control rats. The lower concentration of cytoplasmic RNA was correlated with a decreased ribosomal-RNA content, of which a larger proportion was in the form of free ribosomes. The protein-synthetic competence and messenger-RNA content of isolated ribosomes from liver cells of protein-deprived animals were 40–50% of those noted in controls. At 1hr. after an injection of radioactive uridine, the specific radioactivity of liver total RNA was greater in the group fed on the low-protein diet, but the amount of label that was associated with cytoplasmic RNA or ribosomes was significantly less than that noted in control animals. From these data it was concluded that dietary amino acids regulate hepatic protein synthesis (1) by affecting the ability of polyribosomes to synthesize protein and (2) by influencing the concentration of cytoplasmic ribosomes. It is also tentatively hypothesized that the former process may be directly related to the concentration of cellular free amino acids, whereas the latter could be correlated with the ability of newly synthesized ribosomal sub-units to leave the nucleus.

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