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Study of tRNA in maturing salmon (Oncorhynchus tschawytscha) testes Urquhart, Nadine Iris


During the sexual maturation of salmon testes, there is a drastic decrease in the RNA content of testis tissue and there are marked changes in the type of proteins synthesized. For these reasons, maturing salmon testes seemed an excellent tissue in which to study developmental changes of tRNA populations. Transfer RNA has been isolated from salmon testes at four distinct stages of sexual maturation. Determination of the amounts of tRNA in testes at these four stages of development has shown that during spermatogenesis the testis tRNA population decreases proportionally to that of total testis RNA. Evidence is presented to suggest that the tRNA population of testis tissue is specialized for the synthesis of basic nuclear proteins. Not only was the relative amount of arginine and lysine tRNA extracted from salmon testes found to be significantly greater than tRNA prepared from salmon liver but the relative amount of lysine and arginine tRNA in testis tissue at a specific stage of development seemed adapted to the specific type of basic nuclear protein synthesis occurring at that phase of maturation. These results, together with the results of others suggest that the levels of various tRNAs in cells are altered in a manner consistent with the utilization of various amino acids in protein synthesis. The tRNA[sup Arg] isoacceptors of salmon testes were separated by chromatography on BD-cellulose and RPC-5 columns and their ribosome-binding responses compared in the presence of the six arginine codons which had been synthesized enzymatically. Evidence suggests that of the six tRNA[sup Arg] isoacceptors separated on RPC-5 arginyl-tRNA[sub I] specific for CGA (C,U) and arginyl-tRNA[sub II] specific for codon AGG preferentially increase during the phase of salmon testis maturation in which synthesis of basic nuclear proteins is transformed from mainly histones to mainly protamines. Also, during this research, the effect of temperature, storage, NaCl concentration and ethanol on the extent of charging of salmon testis tRNA by salmon liver arginyl-tRNA synthetase was determined. The Km values of salmon liver arginyl-tRNA synthetase for arginine and salmon testis tRNA were found to be 0.19 µM and 0.76 µM, respectively.

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