Hiro-o Takeshita

Ribonucleic acid metabolism in the posterior silkgland of silkworm, Bombyx mori, during the fifth instar

Abstract RNA metabolism in the posterior silkgland of the silkworm, Bombyx mori L, during the fifth instar has been studied. The base composition of the bulk RNA did not change significantly during the instar. 32 P-pulse labeling during the earlier stage of the instar indicated the synthesis of a rapidly turning-over RNA having a base composition different from that of ribosomal RNA and resembling that of DNA. Sedimentation analysis of RNA at this stage revealed the presence of components having different sedimentation constants from those of the ribosomal and s-RNA. At a later stage of the instar, there was no evidence for the occurrence of a rapidly turning-over RNA having a base composition different from that of ribosomal RNA. The role of RNA in silk fibroin synthesis is discussed.

Nucleic acids accumulation of silk gland of Bombyx mori in relation to silk protein

1. 1. Productivity of silk, properly fibroin, of the silkworm Bombyx mori was in proportion to the amount of RNA accumulation in the posterior division of silk gland. 2. 2. DNA content of the silk gland of a line of high silk productivity was twice as much as that of low productivity. A DNA molecule can transcribe RNA, ranged from 3 × 106 to 6 × 106 molecules. 3. 3. An application of actinomycin to larvae lowered an accumulation of RNA in the silk gland and resulted in a decrease of silk production. 4. 4. Even under the upper limit of starvation by which the larvae complete their life, the silk gland kept a normal level of the DNA content, except that it lost the synthesizing activity of RNA. 5. 5. Treatment of larvae with juvenile hormone occasionally induced another DNA replication of the silk gland.