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A comparison of transcriptional linkage of tRNA cistrons in yeast and E. coli by the ultraviolet light technique.

The ultraviolet light mapping technique was employed to determine the lengths of tRNA cistrons in yeast. The applicability of the method was first tested in the E. coli system, in which the mapping positions for some tRNA cistrons and the ribosomal 5S RNA genes as well as the existence of multimeric transcription units for tRNAs are known. Rates of the synthesis of the tRNAs and small rRNAs after irradiation with various doses of UV light were determined by pulse labeling and quantitation of the RNA species after twodimensional gel electrophoreses. The small ribosomal RNAs served for internal calibration in the estimtion of the target sizes. Our results suggest that--in contrast to the prokaryotic system--in yeast the majority of the tRNA genes are not linked into transcriptional units.