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UBC Theses and Dissertations

A study of tRNA biosynthesis in Escherichia coli Chase, Randal


Escherichia coli was grown in the presence of amino acid analogues or in the absence of required amino acids. The tRNAs. were isolated and characterized. Numerous changes were observed in the total tRNA acceptance for particular amino acids although in no instance did these changes occur for amino acids corresponding to the adverse growth condition. The isoacceptor patterns for particular labelled aminoacyl-tRNAs were determined on the anion exchanger RPC-5. Novel isoacceptor tRNAs were observed under several growth conditions. Significant changes in tRNA isoacceptor distributions were noted. In certain instances it appeared that changes in total amino acid acceptance could be explained in terms of the increased or decreased synthesis of particular tRNA isoacceptors while for other tRNAs it seemed that changes occurred in the synthesis of all isoacceptors for a particular amino acid such that the relative amounts of isoacceptors remained constant even when total amino acid acceptance changed considerably. E. coli was grown over a wide temperature range, 17°C to 44°C, and the tRNA isolated and characterized. Novel tRNA isoacceptors were observed at both high and low growth temperatures for most but not all tRNAs. It was shown that the same isoacceptors could be formed at both extremes of temperature. Preliminary results suggest that the novel isoacceptors are formed as the result of a temperature aggravation of a nutritional problem at extremes of growth temperature. One of the novel tRNA isoacceptors formed under a variety of adverse growth conditions, tRNA3[sup Val] , was purified and partially characterized. The results are consistent with tRNA3[sup Val] being an undermodified precursor of the major isoacceptor tRNA₁[sup Val]. E. coli str[sup D] was grown and the tRNA isolated and characterized. Major differences in the amino acid acceptances for several tRNAs were observed. These changes were accomplished without any significant changes in the relative isoacceptor distributions as determined by RPC-5 chromatography. Gel electrophoretic analysis was performed on tRNA from cells grown at extremes of growth temperature. Significant differences were observed in the 5S region; there was an accumulation of material in cells grown at low temperature and a decrease of material in cells grown at high temperature.

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