Eukaryotic tRNA gene transcription is controlled by signals within and outside the mature coding sequence

We have identified the region within a eukaryotic tRNA gene required for initiation of transcription. These results were obtained by systematically constructing deletions extending from the 5'- or the 3'-flanking regions into a cloned Drosophila tRNAArg gene using nuclease BAL-31. Two control regions within the coding sequence were identified. The first was essential for transcription and was contained between nucleotides 8 to 25 of the mature tRNA sequence. Genes devoid of the second control region, which was contained between nucleotides 50 to 58 of the mature tRNA sequence, could be transcribed but with reduced efficiency. Thus, the promoter regions within a tRNA gene encode the tRNA sequences of the D-stem and D-loop, the invariant U at position 8, and the semi-invariant GTpsi C sequence. While transcription of Drosophila tRNA genes is controlled by signals within the mature tRNA coding region deletion analysis has revealed an oligonucleotide sequence in the 5'-flanking region of a Drosophila tRNA2Lys gene to be responsible for the poor transcriptional activity of this and of other tRNA genes. The oligonucleotide responsible for transcriptional repression is GGCAGTTTTTG and is located 13 nucleotides upstream from the mature tRNA coding sequence. Since the sequence of the undecanucleotide is well conserved within the 5'-flanking region of Drosophila tRNA2Lys genes an investigation of why the transcription of all these genes is not similarly repressed revealed that the position of this oligonucleotide, relative to the mature coding sequence, influences the extent of transcriptional repression.