GENETIC MODULATION OF RNA-METABOLISM IN DROSOPHILA .3. REQUIREMENT FOR AN RDNA-DEFICIENT X-CHROMOSOME IN YBBSUVAR-5-MEDIATED INCREASES IN RNA-SYNTHESIS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 93  (2) , 411-422
Abstract
D. melanogaster males of the genotype car bb/YbbSuVar-5 have an .apprx. 2-fold increase in the rate of accumulation of 4S, 5S, 18S + 28S and poly-A+ RNA molecules when compared to males of the genotype car bb/Ybb- (Clark Strausbaugh and Kiefer, 1977; Clark and Kiefer, 1977). Whether the modulation of RNA metabolism by YbbSuVar-5 requires an r[ribosomal]DNA deficiency on the X chromosome was investigated. Synthetic rates for 4S, 5S and 18S + 28S RNA were measured in the genotypes Sam+iso/Ybb- and Sam+iso/YbbSuVar-5 by injecting adult males with 3H-uridine, allowing them to incorporate label for 2 h, fractionating extracted RNA by polyacrylamide gel electrophoresis and determining the specific activities of RNA (dpm/.mu.gRNA). The synthetic rates for 4S, 5S, and 18S + 28S RNA were the same in these 2 genotypes, demonstrating that the YbbSuVar-5 chromosome does not increase transcription when paired with an X chromosome that is wild type for rDNA. Saturation hybridization was used to measure the rDNA content in several genotypes. Sam+iso/YbbSuVar-5 males and Sam+iso/Ybb- males have equivalent amounts of rDNA. Results are consistent with the suggestion that the Ybb- and YbbSuVar-5 chromosomes have similar amounts of rDNA. The nature of compensatory strategies in rDNA-deficient genotypes is discussed.