Localization of tRNA genes of Drosophila melanogaster by in situ hybridization

Conservatism of sites of tRNA loci among the linkage groups of several Drosophila species

The sites of seven tRNA genes (Arg-2, Lys-2, Ser-2b, Ser-7, Thr-3, Thr-4, Val-3b) were studied by in situ hybridization. 125I-labeled tRNA probes from Drosophila melanogaster were hybridized to spreads of polytene chromosomes prepared from four Drosophila species representing different evolutionary lineages (D. melanogaster, Drosophila hydei, Drosophila pseudoobscura, and Drosophila virilis). Most tRNA loci occurred on homologous chromosomal elements of all four species. In some cases the number of hybridization sites within an element varied and sites on nonhomologous elements were found. It was observed that both tRNA(2Arg) and tRNA(2Lys) hybridized to the same site on homologous elements in several species. These data suggest a limited amount of exchange among different linkage groups during the evolution of Drosophila species.

tRNA(Tyr) genes of Drosophila melanogaster: expression of single-copy genes studied by S1 mapping

Six Drosophila melanogaster tRNA(Tyr) genes have been isolated and sequenced. They contained introns of different sequences and two size classes: 20 or 21 base pairs (bp) (five genes) and 113 bp (one gene). However, the sequences coding for the mature tRNA(Tyr) were identical in all six genes. The 113-bp intron-containing gene was a single-copy gene. Hence, its primary transcript could be traced by S1 mapping. The gene was turned on during embryogenesis and continually expressed to various degrees during the following developmental stages. Thus, S1 mapping is a feasible method to follow the transcriptional activity of individual genes with identical mature products, provided that their primary transcripts are unique. The six genes were organized in two clusters of three and two genes, respectively (each containing a 20- or a 21-bp intron; cytological localization, 85A), and a single-copy gene (113-bp intron; cytological localization, 28C). We show that four of the six tRNA(Tyr) genes characterized were localized in putative 5' control regions of developmentally controlled genes transcribed by polymerase II.

Cloning, sequence analysis and chromosomal localization of the Cu-Zn superoxide dismutase gene of Drosophila melanogaster

The Cu-Zn superoxide dismutase (SOD) cDNA and genomic DNA from Drosophila melanogaster have been isolated. The sequence of the coding region for the Sod gene as well as 413 bp of the 5'-untranslated region, 247 bp of the 3'-flanking DNA, and the single 725-bp intron have been determined [Seto et al., Nucleic Acids Res. 15 (1987) 10601]. The sequence reveals an additional C-terminal triplet coding for valine not found in the mature SOD protein. The nucleotide sequence of the coding region has 56% and 57% homology compared with the corresponding human and rat Sod genes, respectively. The codon usage for the Sod gene is similar to that found for other Drosophila genes. The gene hybridizes to position 68A4-9 on Drosophila polytene chromosomes. In addition, in wild-type Drosophila the Sod cDNA hybridizes to a 0.7-0.8-kb transcript which is greatly diminished in a Sod 'null' mutant that produces only 3.5% of the SOD protein.

tRNA(Tyr) genes of Drosophila melanogaster: expression of single-copy genes studied by S1 mapping

Six Drosophila melanogaster tRNA(Tyr) genes have been isolated and sequenced. They contained introns of different sequences and two size classes: 20 or 21 base pairs (bp) (five genes) and 113 bp (one gene). However, the sequences coding for the mature tRNA(Tyr) were identical in all six genes. The 113-bp intron-containing gene was a single-copy gene. Hence, its primary transcript could be traced by S1 mapping. The gene was turned on during embryogenesis and continually expressed to various degrees during the following developmental stages. Thus, S1 mapping is a feasible method to follow the transcriptional activity of individual genes with identical mature products, provided that their primary transcripts are unique. The six genes were organized in two clusters of three and two genes, respectively (each containing a 20- or a 21-bp intron; cytological localization, 85A), and a single-copy gene (113-bp intron; cytological localization, 28C). We show that four of the six tRNA(Tyr) genes characterized were localized in putative 5' control regions of developmentally controlled genes transcribed by polymerase II.