Mammalian brain ribosomes are behaviourally and structurally heterogeneous

Decrease in ribosomal proteins 1, 2/3, L4, and L7 in Drosophila melanogaster in the absence of X rDNA

The rRNA genes (rDNA) in Drosophila melanogaster are found in two clusters, one on the X and one on the Y chromosome. We have compared the ribosomal protein composition of wild-type Oregon-R flies containing both X-linked and Y-linked rDNA with that of flies containing only the Y-linked rDNA by two-dimensional polyacrylamide gel electrophoresis. Four basic proteins (1, 2/3, L4, and L7) normally present in wild-type flies were either electrophoretically not detectable (1, 2/3, and L4) or marginally detectable (L7) in flies with only Y-linked rDNA. No additional proteins were observed in these flies. However, immunodiffusion assays using specific antibodies raised against purified protein L4 confirmed that L4 was present but in relatively lower amounts in these Y-linked rDNA flies. An investigation was carried out to determine whether these electrophoretically undetectable proteins were more readily lost during ribosome preparation and hence were not readily detectable in the 80S particles by gel electrophoresis or whether they had been modified. Thus the proteins in the post-ribosomal cell supernatant and the high salt sucrose gradient were analyzed by two-dimensional gel electrophoresis and immunochemical assays with antibodies raised against protein L4 and total 80S ribosomal proteins. The experimental evidence indicates that there is a small amount of protein L4 and probably proteins 1, 2/3, and L7 in flies with only Y-linked rDNA but significantly less of these proteins than in wild-type flies.

A comparison of the ribosomal proteins of Drosophila ovary, adult, and embryo

The proteins in the 80S ribosomes of Drosophila melanogaster ovaries and adults have been characterized by two-dimensional polyacrylamide gel electrophoresis. When ribosomal proteins of ovaries and adults were compared with those from embryos, all 3 tissues showed a similar number of proteins. In addition, qualitatively, the electrophoretograms of proteins extracted from the ribosomes of these 3 tissues were found to be indistinguishable. However, apparent quantitative differences in certain acidic proteins were observed between tissues. Using ribosomes from embryos as a standard for comparison, ribosomes from adult flies that were more than 14 days old appeared to have relatively larger amounts of acidic proteins S7 and S9, and relatively smaller amounts of acidic proteins S14 and S25/S27. The transition period occurred during the ninth to thirteenth day of adult fly development. Significant differences were not detected between ovarian and embryonic acidic ribosomal proteins. In contrast to the differential ratio of acidic proteins in ovaries, adults, and embryos, a similar distribution of basic proteins was found in these tissues.

Tissue-specific ribosomal protein composition

Membrane-bound and free polysomes from murine liver and kidney were isolated under identical conditions and their ribosomal proteins were compared by two-dimensional gel electrophoresis. The results demonstrate that these ribosome subpopulations are quantitatively and qualitatively similar except for the presence of one additional protein in the kidney-bound polysomal fraction.

Studies on the effects of chronic ethanol ingestion on the properties of rat brain ribosomes

Previous observations have demonstrated decreased in vivo and in vitro protein synthesis by brain ribosomal systems following long-term ethanol ingestion. For further investigation of the properties of brain ribosomes, the 40S and 60S ribosomal subunits were successfully isolated from control and chronic 10% ethanol-drinking rats. For a successful dissociation of ribosomes into subunits NH4Cl, puromycin and a high-salt treatment at 10 degrees C were essential with a critical concentration of Mg2+ since ribosomes could not be resolved at less than 7 mM Mg2+. Analysis of the A260 profile of the subunits on the sucrose gradients showed no significant differences between the control and ethanol-ingesting groups. Studies on 3H-labeled ribosomes following in vivo RNA labeling showed correspondence of the radioactive profiles from the incorporation of [5(-3) H) orotic acid into RNA with the sucrose gradient absorbance profile of 60S and 40S ribosomal subunits. Furthermore, active reassociation of both subunits occurred at 37 degrees C as demonstrated by the increased [14 C]-phenylalanine incorporation in the presence of poly(U). Results further showed that the poly(U)-dependent [14C]phenylalanine incorporation was significantly reduced by the subunits from the ethanol-ingesting animals. These findings suggest that long-term ingestion of ethanol caused functional changes in the properties of brain ribosomes, specifically on the reassociation process of the two subunits.

Polysome translational state during the cell cycle

HeLa cells were synchronized with a double thymidine block. Ribosomal subunits, monomers and polyribosomes have been quantitatively analysed at hourly intervals, during interphase, and every 15 min, during mitosis. This analysis was performed on linear 7-47% sucrose gradients. From the beginning of G1 up to the end of S phase, a certain equilibrium among ribosomal subunits, monomers and polyribosomes is maintained, while from the time of entering G2 to M the translation machinery appears to be mobilized in the sense of polysome formation. Under these conditions, the amount of polysomes per cell during the mitotic cycle is expressed by a bi-phasic pattern showing pre- and post-mitotic peaks with a falling-off during S. The G1 peak, meanwhile, is much lower than the G2 peak. The incorporation of [3H]leucine into nascent polypeptide chains on polysomes, as well as into bulk cell proteins and into nuclear and cytoplasmic proteins considered separately, is also represented by a bi-phasic curve which shows, however, a higher peak in G1 and a lower peak in G2, with two fallings-off during S and M, respectively. Since between the G1 and the G2 amino acid pools there are not strong differences of leucine concentration, the discrepancy between the amount of polysomes and the rate of labelling is discussed on the basis of the differences of polysome shape found at the different stages of the cycle. In young cells, in fact, there is an abundance of small polysomes, while in the old cell large polysomes predominate. It is suggested that, in the old cell, the rate of translation on large polysomes could be relatively lower or that among these heavy aggregates a given number of "frozen" polysomes could be present. The ribosome state is considered as a probable limiting-factor of translation, particularly in mitosis.