Genetic Modulation of RNA Metabolism in Drosophila. II. Coordinate Rate Change in 4s, 5s, and Poly-a Associated RNA Synthesis

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It has been demonstrated that a particular rDNA-deficient Y chromosome (YbbSuVar-5) increases the rate of ribosomal RNA synthesis in adult testes (Shermoen and Kiefer 1975) and in whole flies (Clark, Strausbaugh and Kiefer 1977). As an initial attempt to explore the molecular basis of this phenomenon, experiments were designed to determine if the rate increase was specific for rRNA as opposed to the other species of RNA. The genotypes used in these studies were car bb/Ybb-, car bb/Y bbSuVar-5, and Sam+ iso. car bb/YbbSuVar-5 and car bb/Ybb- are deficient to the same extent in rDNA and Sam+ iso is a wild-type stock. Following isotope incorporation, total RNA was extracted by a phenol:chloroform method and separated by polyacrylamide gel electrophoresis. The various RNA species were quantified by UV absorption and their radioactivity determined by gel fractionation and liquid scintillation counting. The resulting data permitted the calculation of a specific activity (i.e., dpm/µg RNA) which was defined as synthetic rate. Polyadenylated RNA was isolated using a poly-U sepharose column and similar rate calculations were made. The data from these studies indicate that the rate of synthesis of all species of RNA examined (28S + 18S, 5S, 4S transfer RNA and polyadenylated RNA) is increased by the presence of the YbbSuVar-5 chromosome. Genetic and molecular mechanisms are discussed.

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