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TRANSFER RNA AND THE REGULATION OF PROTEIN SYNTHESIS IN RAT CEREBRAL CORTEX DURING NEURAL DEVELOPMENT
Author(s) -
Harris C. L.,
Maas J. W.
Publication year - 1974
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1974.tb04289.x
Subject(s) - ribosome , ribosomal rna , transfer rna , polysome , rna , biochemistry , protein biosynthesis , enzyme , sephadex , cerebral cortex , biology , microbiology and biotechnology , chemistry , endocrinology , gene
Protein synthesis was measured in ribosomal systems derived from the cerebral cortex of 5‐and 35‐day‐old rats. Under optimal conditions incorporation of radioactive leucine per mg ribosomal protein was four times higher with ribosomes from the younger animals than with ribosomes from the 35‐day‐old rats. This suggests that a decrease in the rate of protein synthesis occurs during neural development. Both ribosomes and the pH enzyme fraction from the cerebral cortex of 35‐day‐old rats had lower activities than preparations from the younger rats. Cerebral cortical ribosomes from 35‐day‐old animals had a lower polyribosome content than similar preparations from 5‐day‐old rats. A three‐fold higher requirement for the pH 5 enzyme fraction was observed with the ribosomal system from 5‐day‐old rats, an observation which correlated with the yields of pH 5 enzyme and ribosomal protein from the younger tissue. The nature of the changes in the composition of the pH 5 enzyme fraction was investigated. Methylated albumin kiesselguhr (MAK) and Sephadex G‐75 column chromatography showed that RNA from the pH 5 enzyme fraction was heterogeneous, containing tRNA, rRNA, and a small molecular weight RNA. This latter RNA, perhaps a degradation product of rRNA, comprised the greatest portion of RNA from the pH 5 enzyme fraction of cerebral cortex. The data obtained with MAK chromatography were used to estimate the total tRNA content of the cerebral cortex, with no age‐related differences being observed. Since evidence of RNA degradation was seen, tRNA was also isolated by phenol extraction of whole cerebral cortex in the presence of bentonite. Purification of tRNA by NaCl and isopropanol fractionation gave preparations with no detectable rRNA or small molecular weight RNA. With this purification method, the tRNA yield was greater than estimated by the MAK method, demonstrating that losses of tRNA occurred during the cell fractionation steps. With the purification method 1.6 times more tRNA was obtained from the cerebral cortex of 5‐day‐old animals than from the older tissue. This higher level of tRNA in the younger, more active tissue appeared to involve all tRNA species, since in vitro aminoacyiation studies revealed nearly identical acceptance values for 18 individual amino acids. These results suggest that the rate of protein synthesis in cerebral cortex is regulated in part by the total amount of tRNA present to translate the higher level of polysome‐bound mRNA.