GENETIC MODULATION OF RNA METABOLISM IN DROSOPHILA. IV. MEASUREMENT OF RATES OF RNA SYNTHESIS BY DENSITY LABELING

Accumulation of RNA was measured in adult males of two genotypes: car bb/Ybb- and car bb/YbbSuvar-5. The two genotypes have similar amounts of rDNA, which is reduced in comparison to wild type (CLARK, STRAUSBAUGH and KIErm 1977). Although genotypically bobbed, car bb/YbbSuVar-5 flies have a wild-type phenotype; car bb/Ybb- flies are both phenotypically and genotypically bobbed (CLARK, STRAUSBAUGH and KIEFER 1977). The wild-type phenotype observed in the car bb/YbbsuVar-5 flies is thought to be the result of an increased rate of rRNA synthesis due ot the presence of the YbbSuVar-5 chromosome (SHERMOEN and KIFFER 1975; CLARK, STRAUSBAUGH and KIEFER 1977; CLARK and KIEFER 1977). To further define this phenomenon, the absolute accumulation of RNA was measured in the two genotypes, using density labeling methods. The accumulation of RNA is 1.4 to 1.8 times higher in car bb/YbbSuVar-5 flies than in car bb/Ybb- flies, demonstrating that there is genetic regulation of synthesis in this genotype. The use of density-labeled nucleosides has clearly shown that there is no difference in precusor pool sizes or use between the two genotypes studied.