The genes coding for tRNA Tyr of Drosophila melanogaster: localization of determination of the gene numbers

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.

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.

Mechanism of suppression in Drosophila: regulation of tryptophan oxygenase by the su(s)+ allele

The suppressor gene, su(s)2, in Drosophila melanogaster restores the production of red and brown eye pigments for some purple and vermilion mutant alleles, respectively. We showed previously that the product of the su(s)+ allele caused inhibition of the sepiapterin synthase A produced by the purple mutant but did not affect the wild-type enzyme. Suppression was accomplished by removing su(s)+ from the genome. We now report that the tryptophan oxygenase, produced by suppressible vermilion alleles, is also inhibited by extracts from su(s)+ flies. The inhibition of the vermilion enzyme can be reduced or eliminated, respectively, by prior storage of the extract at 4 or -20 degrees C or by boiling, whereas the wild-type enzyme is not affected by extracts of su(s)+ flies. Also, when the suppressible vermilion strain is raised on certain diets, brown eye pigment production occurs. This epigenetic suppression was reduced by the presence of an extra copy of su(s)+ in the genome. These data support a posttranslational mechanism for regulation of enzyme activity in which the activity of the mutant enzyme is reduced by the product of the su(s)+ allele. How the su(s)+ gene product can distinguish between the normal and the mutant forms of these two enzymes is discussed, along with other mechanisms for suppression that are currently under investigation.

The genes coding for 4 snRNAs of Drosophila melanogaster: localization and determination of gene numbers

Four small nuclear RNAs (snRNAs) have been isolated from Drosophila melanogaster flies. They have been characterized by base analysis, fingerprinting, and injection into Axolotl oocytes. The size of the molecules and the modified base composition suggest that the following correlations can be made: snRNA1 approximately U2-snRNA; snRNA2 approximately U3-snRNA; snRNA3 approximately U4-snRNA; snRNA4 approximately U6-snRNA. The snRNAs injected into Axolotl oocytes move into the nuclei, where they are protected from degradation. The genes coding for these snRNAs have been localized by "in situ" hybridization of 125-I-snRNAs to salivary gland chromosomes. Most of the snRNAs hybridize to different regions of the genome: snRNA1 to the cytological regions 39B and 40AB; snRNA2 to 22A, 82E, and 95C; snRNA3 to 14B, 23D, 34A, 35EF, 39B, and 63A; snRNA4 to 96A. The estimated gene numbers (Southern-blot analysis) are: snRNA1:3; snRNA2:7; snRNA3:7; snRNA4:1-3. The gene numbers correspond to the number of sites labeled on the polytene salivary gland chromosomes.

Wild-type tRNATyrG reads the TMV RNA stop codon, but Q base-modified tRNATyrQ does not

Although protein synthesis usually terminates when a stop codon is reached along the messenger RNA sequence, there are examples, mainly in viruses, of the stop codon being suppressed by a tRNA species. A strong candidate for this phenomenon occurs in tobacco mosaic virus (TMV) in the form of two proteins (110K and 160K, of molecular weights 110,000 and 160,000, respectively)¹, sharing an N-terminus sequence, which are translated in vitro from a purified species of viral RNA. We have investigated the identity of the tRNA responsible for production of the 160K protein and show here that it is one of the tyrosine tRNAs. Another tyrosine tRNA, in which the first base of the anticodon is highly modified, does not act as a suppressor, indicating the possible regulatory function of such modifications.