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The fluctuation of RNA was determined using the fat body cells of Philosamia cynthia ricini during the course of development from the fifth larval instar to the early pupal stage. The ratio of total RNA to DNA was high in the early fifth instar, but it decreased afterwards to reach a minimum at pupation. This change was mainly accounted for by the reduction of RNA contained in the microsomal fraction. For the purpose of analysing further such changes in RNA, nucleic acids were isolated from the fat body cells by a slightly modified SDS-phenol method after injection of 32P into the body cavity. The sRNA ∗ , rRNA and DNA were fractionated by methylated serum albumin column chromatography. The ratio of sRNA to DNA was rather constant, while the ratio of rRNA to DNA decreased gradually during the progress of development. Incorporation of 32P into sRNA and rRNA took place only in the early stage of the fifth instar. It is concluded that the RNA which exists in the fat body cells in the later stages of the fifth instar and pupal stage was synthesized during the first few days in the fifth larval instar. |
