Modulation of a Drosophila melanogaster tRNA gene transcription in vitro by a sequence TNNCT in its 5' flank.

We have previously demonstrated the existence of both positive and negative transcription modulatory sequences in the 5' flank of a Drosophila melanogaster tRNA(4Val) gene using deletion analysis. The deletion of a pentadeoxynucleotide TCGCT between nucleotides (nt) -34 and -38 relative to the mature coding sequences resulted in a 90% decrease in template activity. In the present study, we have created a number of site-specific changes in the sequence TCGCT. Results indicate a significant decrease in the level of template activity when nt -38(T), -35(C) and -34(T) were mutated. In contrast, a change at nt -37(C) resulted in a slight increase in transcription and a change at nt -36(G) reduced template activity by only 1%. Sequences flanking other tRNA genes which are efficient templates for transcription were examined and found to contain a sequence closely related to TCGCT. We propose that a general form of the sequence TNNCT is a positive transcription modulator for a class of Drosophila tRNA genes.