The Metabolism of Chromosomal Ribonucleic Acid in Drosophila Salivary Glands and its Relation to Synthesis of Desoxyribonucleic Acid

Incorporation of adenine-8-C(14) into chromosomal nucleic acids of Drosophila salivary glands has been observed with the autoradiographic technique. RNA-C(14) and DNA-C(14) were detected as the fractions extractable by ribonuclease digestion and resistant to ribonuclease, respectively. Extractions with desoxyribonuclease and acids were also used to identify the nucleic acids. Time-course curves were determined from grain counts. RNA-C(14) concentration reached a maximum in 2 hours, and decreased after the 4th hour. DNA-C(14) concentration reached its maximum within 8 hours, and showed no decreases during a 48-hour experiment. In the latter part of the period of observation, morphological differentiation of the gland occurred, the decrease in RNA-C(14) became very rapid, and a large increase in DNA-C(14) was observed. Marked decrease in RNA-C(14) and increase in DNA-C(14) were detectable in a few hours when isotope was administered shortly before visible differentiation of the gland. Measurements of nuclear size indicated no significant decreases in RNA-C(14) amount prior to the period of differentiation. During this later period, a large decrease in RNA-C(14) amount occurs suddenly, and the same amount of C(14) is added simultaneously to the DNA fraction, as expected if RNA-C(14) is utilized in the synthesis of DNA.