PROTEIN SYNTHESIS AND THE CONTROL OF PLANT PROCESSES

Bonner , James . (California Inst. Technology, Pasadena.) Protein synthesis and the control of plant processes. Amer. Jour. Bot. 46(1) : 58-62. Illus. 1959.—Microsomal ribonucleoprotein particles which occur in the cytoplasm of plant, animal, and microbial cells alike, possess the function of protein synthesis, and appear to be responsible for the formation of many, perhaps all, of the soluble cytoplasmic proteins. To the process the microsome contributes information, arranging previously acyl-activated amino acid residues in the abundance and sequence characteristic of the specific enzyme being synthesized. The microsome consists of RNA and of protein. The latter appears to be a structural protein, common to microsomes and not directly related to the protein synthesized by the microsome. The amount of information contained in the RNA of a microsomal particle can be calculated to be sufficient for the synthesis of one or at the most a few species of protein molecules. There must therefore be within the cytoplasm of the cell many different species of microsomes, superficially alike, but each different species bearing in RNA code the information required for the assemblage of but one or a few kinds of protein molecules. Microsomes do not, so far as can be judged, possess the power to reproduce. On the contrary microsomal RNA, and possibly microsomal protein also, appear to be synthesized within the nucleus. Transfer of microsomes from nucleus to cytoplasm is therefore implied and is in fact suggested by a variety of indirect experiments. The transfer of nuclear information to the cytoplasm may well be mediated by the microsomes.     

SPECIFICITY OF CREATINE IN THE CONTROL OF MUSCLE PROTEIN SYNTHESIS

This study provides additional evidence that creatine, an end product of contraction unique to muscle, is involved in the control of muscle protein synthesis. Creatine is shown to stimulate selectively the rate of synthesis of two major contractile proteins, actin and myosin heavy chain, in cultures of differentiating skeletal muscle. Creatine affects only the rate of synthesis and not the rate of degradation. Several creatine analogs are as effective as creatine in stimulating muscle protein synthesis, creatinine and amino acids such as arginine and glycine are not. Creatine stimulates myosin heavy chain synthesis twofold in cultures of embryonic muscle grown in either normal or dialyzed media.     

CONTROL OF TREHALASE SYNTHESIS IN NEUROSPORA CRASSA

When an aconidial strain (STL6A) of Neurospora crassa is grown on carbon sources such as glucose, maltose, sucrose, etc., trehalase activity per unit weight of mycelium is very low. By contrast, media containing arabinose, glutamic acid, glycine, etc., which support growth only poorly, produce mycelium with very high trehalase activity. Retarding growth limiting the supply of a necessary nutrient, altering the pH and temperature, or adding toxic substances, however, does not derepress trehalase activity. Repression and derepression of trehalase was found to be reversible through the transfer of cultures to appropriate media. It is likely that the increase in trehalase activity results from de novo synthesis because labeled enzyme can be isolated from acrylamide gels after isolation from medium containing C¹⁴-labeled leucine and after purification by other means. These experiments are interpreted in terms of catabolite repression which may be correlated with events during growth and conidiation.     

STIMULATION BY PHOSPHATE OF THE ACTIVATION OF GLUTAMATE APODECARBOXYLASE BY PYRIDOXYL-5'-PHOSPHATE AND ITS IMPLICATIONS FOR THE CONTROL OF GABA SYNTHESIS

Abstract— Previous studies have shown that inorganic phosphate relieves the inhibition of brain glutamate decarboxylase by ATP. Since the evidence suggested that inhibition by ATP resulted in formation of the inactive apoenzyme, it was possible that P_i might relieve this inhibition by promoting activation of the apoenzyme by its cofactor, pyridoxal-5′-phosphate. We have investigated this possibility using apoenzyme from rat brain. In most experiments, apoenzyme was prepared by incubating glutamate decarboxylase with 20 μM-aminooxyacetate followed by exhaustive dialysis. Activation was studied by incubating the enzyme with pyridoxal-P under various conditions after which the amount of holoenzyme formed was measured by a 5 min enzyme assay. In the absence of P_i there was an initially rapid but incomplete activation by pyridoxal-P which stopped after 15-20 min. The amount of holoenzyme formed after 20 min increased without saturating as the concentration of pyridoxal-P was raised from 0.03 to 250 μm Addition of 1-10mm -P_i increased the initial rate of activation and the final degree of activation. P_i stimulated activation whether present initially or added after 15 min, indicating that incomplete activation in the absence of P_i was not attributable to destruction of pyridoxal-P or irreversible inactivation of the enzyme. P_i reduced the concentration of pyridoxal-P, giving half maximal activation from about 10 μm to about 0.07 μm . Pi also stimulated the residual enzyme activity in the apoenzyme preparation in the absence of added pyridoxal-P, suggesting that P_i may convert the holoenzyme to a more active form. P_i had very similar effects on glutamate apodecarboxylase from vitamin B₆-deficient rats and also stimulated the activation of apoenzyme which had been prepared by dissociation of the cofactor by treatment with glutamate, indicating that stimulation by P_i is unrelated to the method of preparing apoenzyme. Activation was also strongly stimulated by methylphosphonate and arsenate and weakly stimulated by sulfate. Trichloromethylphosphonate, cacodylate, pyrophosphate and AMP had little or no effect. The results suggest that P_i relieves the inhibition by ATP, at least in part, by promoting the activation of glutamate apodecarboxylase, and that P_i may be an important factor in the regulation of glutamate decarboxylase in vivo.     

ELECTRON MICROSCOPE STUDIES ON THE HAEMOGLOBIN MOLECULES

Haemoglobin molecules isolated from normal human subjects have been directly micrographed under the electron microscope following in general Hall's technique. The average height (h) and the widths along (w₁₁) and perpendicular (w) to the shadow direction of the molecules have been measured as 56.5 ± 6.6 A, 122.7 ± 15 A, and 120.9 ± 20 A, respectively. The exaggeration in the molecular widths due to the deposition of metal cap ranges between 60 to 70 A. The probable resolution of the substructure of the molecule, e.g., presence of "holes" and dimples, in the present electron microscopic evidence has been discussed. The electron microscopic results on the size of the individual haemoglobin molecules are in satisfactory agreement with the recent x-ray diffraction model of Perutz and his associates for horse haemoglobin.     

THE OCCURRENCE AND POSSIBLE SIGNIFICANCE OF HAEMOGLOBIN IN THE CHROMOSOMAL REGIONS OF MATURE ERYTHROCYTE NUCLEI OF THE NEWT TRITURUS CRISTATUS CRISTATUS

Absorption measurements in violet light (λ 4047 A) of thin sections of mature newt erythrocytes have indicated the presence of a haem compound, probably haemoglobin, within the chromosomal regions of the nucleus. The amount is about 45 per cent of that in the cytoplasm. The possible significance of this nuclear haemoglobin in determining nuclear structure is discussed in terms of the electrostatic interaction of haemoglobin and nucleohistone.     

复合四倍体异育银鲫的血红蛋白和红细胞的同工酶分析

用聚丙烯酰胺梯度凝胶电泳,分析了银鲫、复合四倍体异育银鲫和红鲁的血红蛋白及红细胞中的４种不同的同工酶。结果表明复合四倍体异育银鲫的一些座位,除了银鲫的基因表达外还观察到红鲤基因的表达,出现了银鲫原来所没有的区带或原有的区带受到抑制等现象,显示出复合四倍体异育银鲫具有类似于杂种的遗传性状,另一方面从４种不同的 同工酶表型分析,表明复合四倍体异育银鲫的同工酶基因表达较接近银鲫。     

STEREOSELECTIVE SYNTHESIS OF 3-HYDROXYMETHYL-D-CYCLOPENTENONE,THE VERSATILE INTERMEDIATE FOR THE SYNTHESIS OF CARBOCYCLIC NUCLEOSIDES

The preparative and stereoselective synthesis (45–50% overall yields, >50 g scale) of the key carbasugars 7a–d was achieved from D-ribose via stereoselective Grignard reaction and oxidative rearrangement as key reactions.     

THE REGULATION OF RNA SYNTHESIS AND PROCESSING IN THE NUCLEOLUS DURING INHIBITION OF PROTEIN SYNTHESIS

The effect of protein synthesis inhibition by cycloheximide on nucleolar RNA synthesis and processing has been studied in HeLa cells. Synthesis of 45S RNA precursor falls rapidly after administration of the drug. However, the nucleolar content of 45S RNA remains relatively constant for at least 1 hr because the time required for cleavage of the precursor molecule into its products is lengthened after treatment with cycloheximide. The efficiency of transformation of 45S RNA to 32S RNA remains constant with approximately one molecule of the 32S RNA produced for each cleavage of a molecule of 45S RNA. However, shortly after the cessation of protein synthesis the formation of 18S RNA becomes abortive. The amount of 32S RNA present in the nucleolus remains relatively constant. After long periods of protein synthesis inhibition the 28S RNA continues to be synthesized and exported to the cytoplasm but at a greatly reduced rate. When the protein synthesis inhibitor is removed, a prompt, although partial, recovery in the synthesis rate of 45S RNA occurs. The various aspects of RNA synthesis regulation and processing are discussed.