Identification of sequences in the 5′ flanking region of a Drosophila melanogaster tRNA 4 Val gene that modulate its transcription in vitro

A TATA element is required for tRNA promoter activity and confers TATA-binding protein responsiveness in Drosophila Schneider-2 cells

In contrast to yeast and mammalian systems, which depend principally on internal promoter elements for tRNA gene transcription, insect systems require additional upstream sequences. To understand the function of the upstream sequences, we have asked whether the Bombyx mori tRNACAla and tRNASGAla genes, which are absolutely dependent on these sequences in vitro, also require them for transcription in vivo. We introduced wild-type and mutant versions of the Bombyx tRNAAla genes into Drosophila Schneider-2 cells and found that the tRNACAla gene is efficiently transcribed and that its transcription depends strongly on the distal segment of its upstream promoter. In contrast, the tRNASGAla gene is inefficiently transcribed, and this inefficiency results from lack of a specific sequence within the distal tRNACAla upstream promoter. This sequence, 5'-TTTATAT-3', is sufficient to increase the activity of the tRNASGAla promoter to that of the tRNACAla promoter. Moreover, promoters containing the 5'-TTTATAT-3' element are stimulated by increased levels of cellular TATA-binding protein. Together these results indicate that, in insect cells, a TATA-like element is specifically required to form functional TATA-binding protein-containing complexes that promote efficient transcription of tRNA genes.

Identification of the transcription start site for the spinach chloroplast serine tRNA gene

Deleting part of the 3' end of the spinach chloroplast serine tRNA coding region, which destroyed the proper folding of its RNA transcript and resulted in the inhibition of tRNA processing, allowed the detection of a serine tRNA primary transcript. The transcription start site for this primary transcript, synthesized from the internal promoter, was mapped to -12 upstream from the mature tRNA coding region. Transcription analysis with various 5' deletion mutants suggested that the AT-rich region between -31 and -11, immediately upstream of the serine tRNA transcription start site, affects the transcription efficiency, and possibly the selection of transcription start site. Identification of the transcription start site for the spinach chloroplast serine tRNA gene in this study represents the first example of 5' end mapping of a tRNA precursor transcribed from chloroplast tRNA genes containing an internal promoter.

The 5'-flanking sequence of the loach oocyte 5S rRNA gene contains a signal for effective transcription

Deletion mutants of loach oocyte 5S rRNA genes were injected and transcribed in vivo in the nuclei of loach (Misgurnus fossilis) and Xenopus laevis. A control region was found in the 5'-flanking sequence, the elimination of which greatly decreases in vivo transcription of 5S rRNA genes. This cis-acting element is located in the region between nt-18 and the transcription start point. We propose that the oocyte nucleus contains (a) specific transcriptional factor(s), NTFO, which interacts with the cis-acting element we described. We also propose that NTFO is inactivated in maturing oocytes when nucleoplasm interacts with oocyte cytoplasm after germinal vesicle breakdown. The residual activity of this factor(s) may be responsible for low-level synthesis of oocyte 5S rRNA at the beginning of embryogenesis. We consider the disappearance of NTFO during gastrulation to be responsible for the total inactivation of oocyte 5S rRNA genes in embryonic and somatic tissue.

Primary structure and functional aspects of the gene coding for the second-largest subunit of RNA polymerase III of Drosophila

We have cloned and sequenced the gene coding for the second-largest subunit of RNA polymerase III of Drosophila melanogaster (DmRP135). The gene, interrupted by two introns of 62 and 59 bp, respectively, codes for an mRNA of 3.6 kb. As for other housekeeping genes transcription initiates at several sites (between positions -98 and -76) none of which is preceded by a clear TATA sequence. The deduced polypeptide consists of 1129 amino acids with an aggregate molecular weight of 128 kDa. The protein sequence features the same regions of similarity as observed for the corresponding subunits of RNA polymerase II of Drosophila and yeast and the Escherichia coli beta subunit. As in the second-largest subunit of RNA polymerase II there is a zinc-binding motif which is absent in the beta subunit of E. coli. Antibodies directed against a fusion protein expressing 164 amino acids of the DmRP135 polypeptide cross-react with the second-largest subunit of RNA polymerase III of yeast and generate a distinct banding pattern on Drosophila polytene chromosomes distinguishable from that obtained with anti-RNA polymerase II antibodies.

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.