Hajime Shigematsu

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.

Biochemical studies on the multiplication of a nuclear-polyhedrosis virus in the silkworm, Bombyx mori: I. Nucleic-acid synthesis in larval tissues after infection

Abstract Tissues of fifth-instar larva of Bombyx mori infected with a nuclear-polyhedrosis virus were compared with healthy tissues as to the activity of protein synthesis, based on the incorporation rate of glycine- 14 C or lysine- 14 C into the proteins. In tissues susceptible to the virus, the activity of the protein synthesis, about 25 hr after virus inoculation, in the infected larva was far higher than that in the normal larva. Eight hours after virus injection, the fat body was the only tissue that kept its high activity throughout the experimental period in the infected larva. In the posterior part of the silk gland, the infection caused a remarkable stimulation of fibroin synthesis within a few hours after virus invasion; this was followed by a prompt repression in activity at Hour 7 of infection, when tissue protein was still continuously being synthesized. Protein extracted from polyhedra isolated from the hemolymph of diseased larvae which had been injected with lysine- 14 C at 3, 25, or 72 hr after virus inoculation, was labeled more distinctly with the hot amino acid at the last period of infection than at the earlier periods.

Biochemical studies on the multiplication of a nuclear-polyhedrosis virus in the silkworm, Bombyx mori: III. Functional changes in infected cells, with reference to the synthesis of nucleic acids and proteins

Abstract Tissues, such as the fat body, susceptible to a nuclear-polyhedrosis virus developed a sequential synthesis of viral DNA, viral messenger RNA, and viral protein almost 50 hr after virus inoculation, and, thereafter, synthesized polyhedron protein until the late period of infection. On the other hand, in such organs as the gut and the posterior part of the silk gland, which resisted virus infection, DNA was synthesized at the beginning of infection, but afterwards, the synthesis of RNA and protein, that were specific for the virus, was insufficient to adversely affect the function of the cell. It was evident from the data pertaining to the incorporation rate of the precursor of each macromolecule that the fat body could synthesize most of the DNA, RNA, and protein required for virus multiplication in a larva. Analysis of the fat body, and consideration of the rate of incorporation of precursor and the amount of the internal pool, showed that the amount of DNA synthesized in the first several hours after virus inoculation was nearly equivalent to the virus titer 5 of LD 50 , and also, the amount of virus protein synthesized between 7 and 50 hr after virus inoculation was close to 5 of LD 50 . The functional alteration was partly visible at the very beginning of the infection as shown by the fibroin synthesis and the “degeneration” of the nucleus supposedly caused by the remarkable synthesis of DNA in the infected cell.

Relationship of crystallization to the nature of polyhedron protein, with reference to a nuclear-polyhedrosis virus of the silkworm, Bombyx mori

Abstract When the silkworm nuclear polyhedrosis inclusion bodies were exposed to a drop of weak alkaline solution, the protein part of the bodies dissolved, and subsequently recrystallized out with the gradual evaporation of water from the preparation under ordinary room condition. The crystals assumed a variety of crystalline forms. These crystalline forms could be demonstrated by a simulation of folding paper strips along the edge or diagonal lines of rhombi which are to be formed on the strips serially by passing parallel lines with an inclination of 60° against the strip edge. Polyhedron protein was very homogeneous and simple in nature, the sedimentation constant being around 6.26 Svedberg units (S). These protein particles were easily associated to form large complexes which gave 13.6, 19.7, 29.7, and 38.0 S in neutral solutions. Associated polyhedron protein complexes were separable into various sizes by ultracentrifuge and disc electrophoresis.

A hydroxy metabolite derived from carbaryl in the silkworm, Bombyx mori

Abstract In silkworms, carbaryl (1-naphthyl- N -methylcarbamate) is metabolized into several metabolites, among which a hydroxy metabolite is the primary intermediate. The hydroxy metabolite has been assigned the structure 2-hydroxy-1-naphthyl N -methylcarbamate on the basis of its physical constants. Output of 14 CO 2 from larvae treated with 14 C-carbaryl is shown to occur concomitantly with the disappearance of the hydroxy metabolite. The correlation between metabolic differences and selective toxicities observed in silkworms and black-tipped leafhoppers is discussed.