Biochemical research on oogenesis. The storage particles of the teleost fish Tinca tinca

Electron microscopic study of crystals of the Xenopus laevis transcription factor IIIA-5S ribosomal RNA complex

A novel method has been developed to grow crystals of the Xenopus laevis transcription factor IIIA-5S RNA complex directly on grids for examination by electron microscopy. Microcrystals were examined in negative stain and in thin sections to reveal a hexagonal lattice with unit-cell dimensions a = b = 87.1 +/- 4.4 A and c = 143.8 +/- 12.7 A. Optical diffraction patterns from micrographs were obtained about the major crystal axes extending to about 40-A resolution. A packing scheme is proposed for which there are three or six transcription factor IIIA-5S RNA complexes in the unit cell related by 3(1) symmetry along the long cell axis. This would require that the 5S RNA molecules are arranged end-to-end, with the terminal loops of adjacent molecules overlapping.

Biochemical research on oogenesis: protein synthesis by purified 42S particles from Xenopus laevis and Tinca tinca previtellogenic oocytes

When incubated with ATP and a labeled amino acid, the 42S particles from early oocytes of Xenopus laevis and Tinca tinca incorporate radioactivity into tRNA and into a high molecular mass material which can be identified as protein. This incorporation is totally independent of ribosomes of cytosolic, mitochondrial or bacterial origin. The incorporated amino acids are linked to a broad spectrum of proteins by covalent bonds. Simple treatments such as incubation in buffer or addition of synthetic polyribonucleotides can inhibit the protein-labeling activity of the particles without affecting their tRNA aminoacylation activity. The former activity corresponds either to an amino acid polymerization reaction or to a protein-modifying reaction of a novel type. No involvement of mRNA in this process has been demonstrated. The alleged amino acid polymerization activity of the 42S particles could be a consequence of the conditions provided to aminoacyl tRNA by the tRNA-binding sites of the particles. These conditions are likely to allow the peptidyl transfer reaction to take place, although at a much lower rate than in the ribosome.

High-performance liquid chromatographic purification of a ribonucleoprotein complex and its protein component

This paper describes the rapid purification by high-performance liquid chromatographic techniques of milligram quantities of the 7 S ribonucleoprotein complex (RNP 7 S) and its protein component from tench (Tinca tinca) oocyte extracts. High-performance gel permeation chromatography (with a TSK 3000SW column) was found to be unacceptable because of multiple contaminants which coelute with RNP 7 S. In contrast, semipreparative high-performance DEAE ion-exchange chromatography was found to give an excellent separation of the 7 S complex which could be directly adapted to a preparative scale providing rapid purification (less than 1 h) of milligram quantities of the complex. Agarose electrophoresis followed by specific staining of protein and nucleic acid was found to be a convenient and rapid means of evaluating the purification. Finally, reverse-phase high-performance liquid chromatography was found suitable for the purification of the protein component of the 7 S complex.

Analysis of reconstruction of an RNP particle which stores 5S RNA and tRNA in amphibian oocytes

Previtellogenic oocytes of Triturus cristatus accumulate a free cytoplasmic RNP which sediments at 40S and contain 5S RNA and tRNA in association with two proteins of MW 45,000 and 39,000 daltons (P45 and P39). The 40S particle has a buoyant density of 1.53 g . cm-3 in CsCl and consists of four identical RNP subunits. Each monomeric subunit contains one molecule of 5S RNA, three molecules of tRNA, two molecules of P45 and one molecule of P39. The 40S particle can be completely dissociated by SDS treatment into its individual components, and the subunits, and even the complete 40S particle, can be reformed by removal of SDS in the presence of 0.2 M NaCl. RNA/protein binding experiments with isolated components, and analysis of reformed RNP complexes in CsCl gradients, demonstrate that the stable interactions are: 5S RNA/P45, 3(tRNA)/P45, 5S RNA/P39 and 5S RNA/P45/P39. Immunological studies show that P45 has also a nuclear location and may bind to the 5S RNA transcript in the chromatin, whereas P39 is predominantly cytoplasmic and is possibly related to proteins associated with 5S RNA in the ribosomal 60S subunit. It is suggested that the 40S RNP particle not only stores 5S RNA and tRNA but also provides a means for the exchange of the 5S RNA transcript binding protein (P45) for the 5S RNA ribosome associated protein (P39).

Biochemical Research on oogenesis. Composition of the 42-S storage particles of Xenopus laevix oocytes

Previtellogenic oocytes of Xenopus laevis contain far more 5-S RNA and tRNA than 28-S + 18-S RNA. tRNA and 5-S RNA are storage products that will be used in later oogenesis for protein synthesis and ribosome assembly. Stored tRNA and 5-S RNA are not free in the cell sap but belong to nucleoprotein particles of various sizes. There are two prominent kinds of storage particles in previtellogenic oocytes of X. laevis. The smaller ones (7-S) contain about half of the cell's 5-S RNA. The larger ones (42-S) contain the remainder of the 5-S RNA and 90% of the tRNA. The 7-S particles consist of one molecule of 5-S RNA and one molecule of protein. In this paper we describe the biochemical and physical properties of the 42-S particles. The 42-S particle contains four main components: tRNA, 5-S RNA, a 50000-Mr protein (a) and a 40000-Mr protein (b) in the following molar ratios: 3/1/2/1. We propose a 28-component model for the 42-S particles. This model is consistent with all the biochemical and physical data that we report here. A 42-S particle is made up of four subunits, each of which contains three molecules of tRNA, one molecule of 5-S RNA, two molecules of protein a, and one molecule of protein b. Protein b from the 42-S particles and the 7-S particle protein are indistinguishable by all tests that we have tried. We present evidence showing that protein a binds tRNA whereas protein b binds 5-S RNA in the 42-S particles as well as in the 7-S particles.