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Studies on transfer RNA and transfer RNA genes in Drosophila melanogaster Dunn, Robert James


In the present study Drosophila melanogaster was used to define the organization and expression of tRNA genes. The three major Drosophila valine tRNAs were isolated and purified by standard chromatographic techniques. Nucleoside analysis indicated that of these tRNAs only tRNA₄Val contained inosine. All three tRNAsVal contained ribothymidine, therefore they resemble yeast tRNAVal in this regard but not the mammalian tRNAsVal which lack ribothymidine. The purified tRNAs were labelled with ¹ ² ⁵I and used to determine the location of the genes for these tRNAs utilizing the technique of in situ hybridization to salivary gland chromosomes. tRNA₄Val hybridized consistently to one site on the right arm of the second chromosome, 56D, which is close to the site of 5S RNA, 56F. tRNA₃bVal hybridized to two sites, 84D and 92B, both on the right arm of the third chromosome. The labelling of site 84D was approximately twice as heavy as that of 92B. Dr. A. Delaney (unpublished) has shown that approximately 13 genes code for tRNA₃bVal per haploid genome. The in situ hybridization data suggests that the 13 genes are divided such that approximately 8 genes are at site 84D and 5 genes are at site 92B. Evidence to support this supposition is derived from measurements on the amount of tRNA₃bVal in mutant flies deficient or duplicated for site 84D on one of their two homologous third chromosomes. tRNA₃bVal amounts, measured relative to the other tRNAVal isoacceptors decrease 31% in the deficiency and increase 30% in the duplication. These results demon- strate a direct relationship of the amount of tRNA₃bVal to gene dosage because the duplication has 8 extra genes, which is a 30% increase and the deletion has 8 fewer genes, a 30% decrease. Finally, it was shown that the amount of total tRNSVal increased by 17% in the duplication but did not decrease in the deletion. This result demonstrates the amount of valine tRNA is under a type of control in which the amount of total valine tRNA is increased to compensate for the deficiency of a single isoacceptor. Also the coding properties of four tRNASer isoacceptors were determined.

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