Stimulation of transcription of the yeast tRNATyr gene in cell-free extracts by tyrosyl-tRNA synthetase

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Abstract
Eukaryotic transfer RNA genes have two internal discontinuous control regions, the A and B blocks, which correspond approximately to the D-stem and the pseudo-U arm of tRNA. In reconstituted transcription systems at least two components are required to direct accurate initiation by RNA polymerase (refs 4,5). However, little is known about the mechanism of interaction of the internal promoter sequences with factors and RNA polymerase C within the transcription complex, although tRNA-like conformation of the B block sequence was surmised to be critical for DNA recognition. By analogy with the 5S RNA system, where a transcription factor required for 5S DNA expression was shown to interact both with 5S RNA and with the noncoding strand of the 5S gene, we explored the possibility that a protein which normally binds to tRNA could also interact with the tRNA gene and regulate its transcription. Here we show that in vitro transcription of the yeast SUP4 tRNATyr gene in crude yeast extracts is strongly stimulated by tyrosyl-tRNA synthetase (TyrRS) but not by two other non-cognate synthetases. Substrates of the synthetase, tRNATyr and tyrosine, interfere with stimulation of tRNA synthesis.