[Ribonucleoprotein-particles from telotrophic meroistic ovary ofDysdercus intermedius Dist. (Heteroptera, Pyrrhoc.) and their behaviour in a cell-free protein synthesizing system].

Abstract

In the telotrophic meroistic ovary ofDysdercus intermedius Dist. the oocyte is provided in a previtellogenic state with RNP-particles synthesized by trophocytes, transported in nutritive cords and deposited in oocytes. Ribosomes prepared by differential centrifugation from trophic tissue and mature eggs were fractionated into RNP-particle classes using a linear sucrose gradient. Particles were labeled by injecting radioactive RNA-precursors. Two hours later in trophic tissue besides 80 s monosomes and ribosomal subunits labeled RNP-particles are detected sedimenting slower than small ribosomal subunits (10-40 s). They are not transferred into the polyribosomal protein synthesizing complex of trophocytes. The ribosome fraction from eggs laid 8 days after injection of radioactive precursor contains the same labeled RNP-particle groups as the trophocytes. Because of the special character of telotrophic meroistic insect ovary (no detectable synthetic activity of oocyte nuclei during the growth phase, no contribution of high molecular weigth RNA from follicle cells to oocyte) these particles in the fresh laid bug-egg can be considered as products which are synthesized in trophocytes and therefore as depot-forms of maternal information for early embryonic protein synthesis.80 s monosomes contain exclusively rRNA (28 s and 18 s). In the slow sedimenting RNP-particles RNA was detected showing the following mRNA-characteristics: 1. a heterogenic molecular size with maximum at 7-9 s (proved by gelelectrophoretic analyses of radioactive labeled RNA isolated from particle groups), 2. a high content of Poly A-segments (proved by retention on nitrocellulose filters), 3. a stimulating capacity on amino acid incorporation in a cell-free protein synthesizing system.In a homologous cell-free system composed of bug components native mRNP-particles (10-40 s) from eggs and nurse cells cause an inhibition of amino acid incorporation into proteins. For this inhibitory effect proteins are responsible which dissociate from the particles in a medium of high ionic strength (0.5 M KCl). Under the same experimental conditions factors are dissociated from larval RNP-particles which show a stimulating effect on amino acid incorporation. Therefore inhibitory factors are thought to be structural or accessory specific components of maternal mRNP-particles. M-RNA from egg particles freed from inhibitory factors can be translated by specific factors which are detected-like the inhibitors in the ribosomal wash fraction.