Isolation of Polyribosome from Tobacco Plants Infected with Tobacco Mosaic Virus

Polyribosomes have been isolated from tobacco leaves. Upon infection with TMV, a new polyribosome has appeared which is specific for infection, and TMV-antigenic protein is formed on this polyribosome. This new polyribosome has an S-value of 360–380. From these results, it is suggested that this TMV specific polyribosome is an aggregate of 60–80 ribosomes which is bound by TMV-RNA as messenger, and that TMV-RNA is translated polycistronically.     

Effect of Diethyl Pyrocarbonate Modification of Benzodiazepine Receptors on [3H]Ro 15-4513 Binding

The effects of treatment of brain membranes with diethyl pyrocarbonate (DEP), a histidine-modifying reagent, on the binding of 3H-labeled Ro 15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a]- [1,4]benzodiazepine-3-carboxylate) and [3H]diazepam were compared. DEP pretreatment produced a dose-dependent decrease in [3H]diazepam binding, whereas low DEP concentrations enhanced the binding of [3H]Ro 15-4513. These effects were reversed by incubation with hydroxylamine after the treatment. The enhancement of [3H]Ro 15-4513 binding was due to an increase in the affinity of the binding sites (KD), without any effect on binding capacity (Bmax). The enhancement was perceived in cerebral cortical, cerebellar, and hippocampal membranes. DEP treatment decreased the displacement of [3H]Ro 15-4513 binding by diazepam and FG 7142 (N-methyl-beta-carboline-3-carboxamide) but not by Ro 15-4513 and Ro 19-4603 (tert-butyl-5,6-dihydro-5-methyl-6-oxo-4H-imidazol[1,5- a]thieno[2,3-f][1,4]diazepine-3-carboxylate). Although the stimulating effect of gamma-aminobutyric acid (GABA) on [3H]-diazepam binding was not affected by DEP treatment, such treatment reduced the inhibitory effect of GABA on [3H]Ro 15-4513 binding. The enhancement of [3H]Ro 15-4513 binding was observed in membranes pretreated with DEP in the presence of flunitrazepam, whereas such pretreatment reduced significantly the inhibitory effect of DEP on [3H]-diazepam binding.(ABSTRACT TRUNCATED AT 250 WORDS)     

烟草愈伤组织生长和衰老过程中多聚核糖体类群的变化(英文)

本研究中测定了黄花烟草(Nicotiana rusticaL cv.Gansu yellow flower)愈伤组织生长和由碳水化合物亏缺引起的衰老过程中多聚核糖体类群和蛋白质含量的变化,以期查明衰老的烟草愈伤组织中蛋白质合成速率与蛋白质含量变化的相关性。 继代培养的烟草愈伤组织经过约5d的生长迟滞期,进入指数生长期,第20天后生长停止,干重缓慢下降;第25天出现类似果实成熟时的呼吸跃变现象,呼吸商(RQ)开始下降,呼吸底物由糖转向游离氨基酸,表明在本实验条件下,烟草愈伤组织在培养20～25d后由生长转向衰老,这时蛋白质含量(占细胞总蛋白的90％～95％)立即降低,第35天降低了26％。代表蛋白质合成能力的多聚核糖体相对含量和总核糖体的相对含量在培养20d后开始减少;两者的比值也降低,这与植物衰老过程中蛋白质含量的降低基本一致,表明烟草愈伤组织衰老过程中蛋白质含量的降低.与蛋白质合成能力的下降可能有一定的关系。由于多聚核糖体的解聚并不伴随有单核糖体的增加,也暗示衰老过程中单核糖体被迅速破坏。     

Polyribosome distribution in regenerating livers of irradiated adrenalectomized rats.

The effect of gamma-radiation (1800 rad) on polyribosome distribution in the regenerating livers of intact and adrenalectomized rats was studied both before and after partial hepatectomy. The animals were divided into four sub-groups: (1) control; (2) irradiated only; (3) partially hepatectomized; and (4) irradiated partially hepatectomized. The relative distribution of lighter oligosomes to heavier polyribosomes was analysed by sucrose density gradient centrifugation (10-40 per cent). Partial hepatectomy by itself increased the proportion of heavier polyribosomes in both intact and adrenalectomized rats. However, when gamma-rays were delivered 2 hours before or 2 hours after partial-hepatectomy, the formation of heavy polyribosomes was decreased for at least 24 hours after hepatectomy in the adrenal intact rats. This depression was not maintained until later times (48 and 72 hours after hepatectomy) when an increase in the proportion of heavy polyribosomes relative to light oligosomes was observed. In addition, irradiation did not measurably affect the distribution of polyribosomes in regenerating hepatocytes of adrenalectomized rats at any time after partial hepatectomy.     

Polyribosome size analysis. Measurement of number-average polyribosome sizes

The analysis of translational efficiencies of specific mRNAs requires a determination of the polyribosome size. The appropriate value to use in such calculations is the number-average size. A method is described for accurately measuring the number-average size of total and of specific protein synthesizing polyribosomes using isokinetic sucrose density gradients and 125I-labeled antibodies. By this method, we demonstrated that albumin synthesizing polyribosomes from a serum albumin secreting mouse hepatoma cell line exist over a broad range from trimers to 20-mers (mean 6-10). The specificity of antibody interaction with polyribosomes was demonstrated using cells not synthesizing mouse serum albumin, and by demonstrating that 125I-anti ovalbumin does not bind to mouse hepatoma polyribosomes. Treatment of the mouse hepatoma cells with 1 MUM cycloheximide shifted practically all of the monomers into polyribosomes resulting in an increase in the number-average size of the albumin synthesizing polyribosomes. Cycloheximide treatment, however, did not eliminate the size heterogeneity in the albumin synthesizing polyribosomes.     

Effects of Hypoglycemia on Rat Brain Polyribosome Sedimentation Pattern

Insulin-induced hypoglycemia provokes polyribosome disaggregation and accumulation of monomeric ribosomes in the brain of rats with hypoglycemic paresis and coma. The extent of brain polyribosome disaggregation depends on the decrease of blood glucose concentration, and in comatose animals on the duration of hypoglycemia. Cycloheximide prevents the disaggregation of brain polyribosomes induced by hypoglycemia, indicating that hypoglycemia affects brain protein synthesis, decreasing the rate of initiation relative to the rate of elongation of polypeptide chain synthesis.     

Polyribosome Content in Young and Aged Wheat Leaves Subjected to Drought

The effect of a droughting treatment on the polyribosome contentof wheat leaves was markedly different on leaves of differentages. Growing leaves showed a large decrease in their polyribosomepopulation, while fully expanded leaves showed no loss of polyribosomescompared with controls. These results suggest that the largereductions in polyribosome population observed in growing tissuesare due to reductions in growth, rather than a direct effectof water stress.     

Polyribosome metabolism in Escherichia coli starved for an amino acid

Most polyribosomes are inferred to be inert in starving cells, but some are in a dynamic state, since (1) messenger RNA continues to enter polyribosomes; (2) about 20 to 40% of the polyribosomes are labile after rifampycin addition; (3) β-galactosidase can be induced with a lag period no more than three times as long as in growing cells; and (4) the apparent rate of synthesis of protein chains, judged by the distribution of pulse-labeled protein between ribosomes and soluble protein, is about half that in growing cells.     

Within-day Changes in the Polyribosome Content and in Synthesis of Proteins in Leaves of Capsicum annuum L

Capsicum annuum cv. California Wonder was grown in controlled environment with a 12-hour photoperiod. The polyribosome content of leaves varied from 60 to 72% of total ribosomes with the highest level occurring in the middle of the photoperiod and the lowest in the middle of the dark period. The variation was accounted for by changes in the content of large polyribosomes (hexamers and larger). There was no indication of an immediate effect on polyribosome content of light-on or light-off.

The synthesis of proteins at two times in the 24-hour cycle was compared using a dual isotope technique. Statistically significant results were obtained that suggested that protein(s) with molecular weights of 26,000 daltons were preferentially synthesized in the photoperiod compared to the dark period. No evidence was found for the differential synthesis of proteins within the photoperiod.

     

Water Potential, Growth, and Polyribosome Content of the Stressed Wheat Apex

The effect of drought on the growth, ribosomal content, andwater potential of the immature floral apex of wheat plantswas studied under controlled environment conditions. Duringdrought the water potential of the apex (measured with a thermocouplepsychrometer) decreased at approximately the same rate as thatof expanded leaves. Elongation and differen tiation of the floralapex ceased at approximately –12 x 10⁵ Pa and the polyribosomalcontent decreased from 50% of the total ribosomal populationto less than 10%. At this water potential also, elongation ofexpanding leaves was severely inhibited. With continued drought the water potential of the apex continueddecreasing. The exposed leaves died at a water potential ofabout –35 x 10⁵ Pa but the apex was still alive at a waterpotential of –60 x 10⁵ Pa and after rewatering it eventuallyresumed growth.     

Isolation of rat hepatocyte plasma membranes. I. Presence of the three major domains

A rat liver plasma membrane preparation was isolated and characterized both biochemically and morphologically. The isolation procedure was rapid, simple and effective in producing a membrane fraction with the following biochemical characteristics: approximately 40-fold enrichment in three plasma membrane markers, 5'-nucleotidase, alkaline phosphodiesterase I (both putative bile canalicular membrane enzymes), and the asialo-glycoprotein (ASGP) receptor (a membrane glycoprotein present along the sinusoidal front of hepatocytes); a yield of each of these plasma membrane markers that averaged approximately 16%; and minimal contamination by lysosomes, nuclei, and mitochondria, but persistent contamination by elements of the endoplasmic reticulum. Morphological analysis of the preparation revealed that all three major domains of the hepatocyte plasma membrane (sinusoidal, lateral, and bile canalicular) were present in substantial amounts. The identification of sinusoidal membrane was further confirmed when ASGP binding sites were localized predominantly to this membrane in the isolated PM using electron microscope autoradiography. By morphometry, the sinusoidal front membrane accounted for 47% of the total membrane in the preparation, whereas the lateral surface and bile canalicular membrane accounted for 6.8% and 23% respectively. This is the first report of such a large fraction of sinusoidal membrane in a liver plasma membrane preparation.     

Polyribosome formation and protein synthesis in imbibed but dormant lettuce seeds

Dormancy is maintained in Grand Rapids lettuce (Lactuca sativa) seeds imbibed on water in darkness at 25 C. Polyribosome formation and protein synthesis occur early in the imbibition phase and considerable polysomal material is also present after 24 and 48 hours, even though the seeds have failed to germinate. Incorporation of labeled leucine into protein following a 24-hour preincubation period shows that these polysomes are active in protein synthesis.