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1.
The binding of spermine to the ribosomes and ribosomal ribonucleic acid from Bacillus stearothermophilus 总被引:8,自引:3,他引:5
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L. Stevens 《The Biochemical journal》1969,113(1):117-121
1. The total intracellular concentrations of Na(+), K(+), Mg(2+), spermine, spermidine and RNA were measured in Bacillus stearothermophilus. 2. The binding of spermine to ribosomes and to ribosomal RNA from B. stearothermophilus was studied under various conditions by using a gel-filtration technique. 3. The affinity of spermine for ribosomes and for ribosomal RNA decreased with increasing ionic strength of the medium in which they were suspended. 4. The extent of spermine binding did not change appreciably in the temperature range 4-60 degrees . 5. Optimum binding occurred at about pH7.0. 6. The number of binding sites for spermine on either ribosomes or ribosomal RNA was 0.10-0.13/RNA phosphate group. 7. A high proportion of the intracellular spermine is likely to be bound to the ribosomes in vivo; spermine competes with Mg(2+) on equal terms for sites on the ribosomes. 相似文献
2.
The location of spermine in bacterial ribosomes as indicated by 1,5-difluoro-2,4-dinitrobenzene and by ethidium bromide 总被引:2,自引:0,他引:2
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1. When the binding of ethidium bromide to rRNA is measured both in the presence and in the absence of spermine, by spectrophotometric titrations, by gel filtration, or by the changes in fluorescence intensity, spermine competes with ethidium bromide for sites on the rRNA; under the conditions used in these experiments ethidium bromide is bound to the double-stranded regions of rRNA. 2. When an excess of ethidium bromide is added to ribosomes from Bacillus stearothermophilus approx. 80% of the endogenous spermine is displaced from the ribosomes. 3. [(14)C]Spermine is fixed to ribosomes by either formaldehyde or 1,5-difluoro-2,4-dinitrobenzene. Most of the [(14)C]spermine, fixed to ribosomes by 1,5-difluoro-2,4-dinitrobenzene, attaches to the ribosomal protein. 4. It is concluded that most of the endogenous spermine is bound to the double-stranded RNA in ribosomes, and that some of these double-stranded regions to which spermine is attached also have ribosomal proteins bound to them. 相似文献
3.
Ribonucleic acid and ribosomes of Bacillus stearothermophilus 总被引:16,自引:7,他引:9
Saunders, Grady F. (University of Illinois, Urbana), and L. Leon Campbell. Ribonucleic acid and ribosomes of Bacillus stearothermophilus. J. Bacteriol. 91:332-339. 1966.-The ability of some thermophilic bacteria to grow at temperatures as high as 76 C emphasizes the remarkable thermal stability of their crucial macromolecules. An investigation of the ribonucleic acid (RNA) and ribosomes of Bacillus stearothermophilus was conducted. Washed log-phase cells were disrupted either by sonic treatment or by alumina grinding in 10(-2)m MgCl(2)-10(-2)m tris-(hydroxymethyl)aminomethane buffer, pH 7.4 (TM buffer). Ultracentrifugal analysis revealed peaks at 72.5S, 101S, and 135S, with the 101S peak being the most prominent. By lowering the Mg(++) concentration to 10(-3)m, the ribosome preparation was dissociated to give 40S, 31S, and 54S peaks. These in turn were reassociated in the presence of 10(-2)m Mg(++) to give the larger 73S and 135S particles. When heated in TM buffer, Escherichia coli ribosomes began a gradual dissociation at 58 C, and at 70 C underwent a large hyperchromic shift with a T(m) at 72.8 C. In contrast, B. stearothermophilus ribosomes did not show a hyperchromic shift below 70 C; they had a T(m) of 77.9 C. The thermal denaturation curves of the 4S, 16S, and 23S RNA from both organisms were virtually identical. The gross amino acid composition of B. stearothermophilus ribosomes showed no marked differences from that reported for E. coli ribosomes. These data suggest that the unusual thermal stability of B. stearothermophilus ribosomes may reflect either an unusual packing arrangement of the protein to the RNA or differences in the primary structure of the ribosomal proteins. 相似文献
4.
CYTOCHEMICAL STUDY ON THE PANCREAS OF THE GUINEA PIG : VII. Effects of Spermine on Ribosomes
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Pancreatic ribosomes (guinea pig) aggregate and lose upon treatment with polyamines, particularly spermine, their bound secretory enzymes. Spermine, at 0.5 mM, for example, causes the release of about 85 per cent of the chymotrypsinogen and RNase, and from 85 to 100 per cent of the ribosomal amylase. At the same time, the particles lose about 10 per cent of their RNA, 7 to 24 per cent of their total protein, and from 75 to 100 per cent of their Mg++. Observations with the electron microscope confirm the heavy agglutinating of the ribosomes but otherwise show little change in the structure of the particles. Using radioactive spermine it was found that, concomitant with the loss of bound enzymes and Mg++ from the ribosomes, spermine became bound to the particle. The extent of binding ranged from 0.29 to 1.49 µmoles per 10µmoles RNA-P. The bound radioactive spermine can be removed by subsequent treatment of the ribosomes with GTP, ATP, or P-P, which treatment also removes most of the RNA of the particles, leaving behind ribosomes with a much lower RNA/protein ratio. From this evidence it was inferred that spermine, in releasing the Mg++ of the particle, becomes salt-linked to the free phosphate hydroxyl groups of the RNA. Freshly isolated pancreatic and hepatic ribosomes contain very little spermine, about 0.1 to 0.2 µmoles polyamine/10 µmoles RNA-P. The results are discussed in terms of the linkages between the structural protein, the bound secretory enzymes, and the RNA of the ribosomes. 相似文献
5.
Exposure of Escherichia coli MRE-600 ribosomes to acridine orange (AO) at low ionic strength (1mM Tris-acetate pH 7.4) results in quantitative binding of the dye. Under our experimental conditions about a few hundred dye molecules can be bound to any one of the 30, 50, or 70-S particles. AO causes the 30 and the 50-S subunits to form ribosomal aggregates of approximate sedimentation constants of 70 and 100-S. 相似文献
6.
The effect of spermine on the inhibition of peptide-bond formation by clindamycin, an antibiotic of the Macrolide-Lincosamide-StreptograminsB family, was investigated in a cell-free system derived from Escherichia coli. In this system peptide bond is formed between puromycin, a pseudo-substrate of the A-site, and acetylphenylalanyl-tRNA, bound at the P-site of poly(U)-programmed 70 S ribosomes. Biphasic kinetics revealed that one molecule of clindamycin, after a transient interference with the A-site of ribosomes, is slowly accommodated near the P-site and perturbs the 70 S/acetylphenylalanyl-tRNA complex so that a peptide bond is still formed but with a lower velocity compared with that observed in the absence of the drug. The above mechanism requires a high temperature (25 degrees C as opposed to 5 degrees C). If this is not met, the inhibition is simple competitive. It was found that at 25 degrees C spermine favors the clindamycin binding to ribosomes; the affinity of clindamycin for the A-site becomes 5 times higher, whereas the overall inhibition constant undergoes a 3-fold decrease. Similar results were obtained when ribosomes labeled with N1-azidobenzamidinospermine, a photo-reactive analogue of spermine, were used or when a mixture of spermine and spermidine was added in the reaction mixture instead of spermine alone. Polyamines cannot compensate for the loss of biphasic kinetics at 5 degrees C nor can they stimulate the clindamycin binding to ribosomes. Our kinetic results correlate well with photoaffinity labeling data, suggesting that at 25 degrees C polyamines bound at the vicinity of the drug binding pocket affect the tertiary structure of ribosomes and influence their interaction with clindamycin. 相似文献
7.
Effect of polyamines on the stability of brain-cortex ribosomes 总被引:3,自引:3,他引:0
1. Ribosomes isolated from the cortex tissue of goat brain contain very small amounts of spermidine and spermine. Ribosomes isolated from spermidine-treated slices have a higher spermidine content. 2. The polyamines partially prevent the temperature-dependent breakdown of ribosomes into acid-soluble nucleotides. 3. The ;melting' temperature of ribosomes rises slightly when the ribosomes are heated slowly in the presence of polyamines. 4. The pH-dependent breakdown of ribosomes into protein, RNA and acid-soluble nucleotide is markedly decreased by polyamines present in media in which ribosomes are suspended. 5. The breakdown of ribosomes in the presence of high concentrations of salts and EDTA is partially checked by the concurrent presence of polyamines. 6. Spermidine and spermine make ribosomes less susceptible to enzymic digestion by crystalline trypsin and ribonuclease. 相似文献
8.
Stability of ribosomes and ribosomal ribonucleic acid from Bacillus stearothermophilus 总被引:7,自引:3,他引:4
After heating at 65 C, ribosomes isolated from Bacillus stearothermophilus were strikingly more heat-stable than comparable preparations from Escherichia coli when tested for ability to support polyuridylic acid-directed phenylalanine incorporation at 37 C. The stability of ribosomes was also determined by measurements of hyperchromicity at 259 mmu while heating them from 25 to 90 C. In standard buffer containing 0.01 m Mg(++), the T(m) (temperature at the midpoint of total hyperchromicity) of E. coli and B. stearothermophilus ribosomes was 71 and 81 C, respectively. In a magnesium-free buffer, the T(m) of E. coli and B. stearothermophilus ribosomes was 44 and 64 C, respectively. Putrescine (0.01 m) was more effective in stabilizing ribosomes from B. stearothermophilus than those from E. coli. Spermidine (0.001 m), on the other hand, was more effective in stabilizing ribosomes from E. coli than those from B. stearothermophilus. Melting curves of total ribosomal ribonucleic acid (rRNA) from E. coli and B. stearothermophilus revealed T(m) values of 50 and 60 C, respectively. Putrescine stabilized thermophile rRNA, but had no effect on E. coli rRNA. Sucrose density gradients demonstrated that thermophile 23S ribonucleic acid was degraded during storage at -20 C; the 23S component from E. coli was stable under these conditions. The results are discussed in terms of the mechanism of ribosome heat stability and the role of the ribosome in governing the temperature limits for bacterial growth. 相似文献
9.
Preparation of ribosome-free membranes from rat liver microsomes by means of lithium chloride 总被引:5,自引:4,他引:1
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1. Treatment of washed rat liver microsomes in a medium containing 0.12m-sucrose, 12.5mm-potassium chloride, 2.5mm-magnesium chloride and 25mm-tris-hydrochloric acid buffer, pH7.6, with 2m-lithium chloride at 5 degrees for 16hr. leads to the formation of membranes free of ribosomes and ribosomal subunits. 2. Confirmation of the absence of ribosomes from lithium chloride-prepared membranes was obtained by treatment of the membranes with sodium deoxycholate, followed by sucrose-density-gradient centrifugation, which showed the complete absence of ribosomes. 3. Treatment of membranes with phenol, followed by sucrose-density-gradient analysis of the isolated RNA, showed the presence of a small amount of 4s material. Repetition of the phenol extraction procedure in the presence of liver cell sap as a ribonuclease inhibitor again showed the presence of only 4s material. The 4s RNA was shown to be transfer RNA by the fact that it had the same capacity for accepting (14)C-labelled amino acids as isolated transfer RNA from rat liver pH5 enzyme. 4. Analysis showed that microsomes and membranes possessed similar glucose 6-phosphatase, NADH-2,6-dichlorophenol-indophenol reductase, NADH-neo-tetrazolium reductase, NADH-cytochrome c reductase and ribonuclease activities. 5. (3)H-labelled ribosomal RNA binds to membranes. However, isolation of the bound RNA by the phenol extraction procedure, followed by sucrose-density-gradient analysis, shows the RNA to be degraded to 7s material. Very little breakdown of (3)H-labelled ribosomal RNA bound to membranes occurs if the binding and isolation are carried out in the presence of liver cell sap. 相似文献
10.
1. The polyamines, putrescine, spermidine and spermine occur in free or acetylated form in a wide variety of living organisms. Putrescine is biosynthesized from ornithine or arginine; spermidine and spermine from methionine and either ornithine or arginine. 2. It is difficult to determine the intracellular distribution of polyamines since they are all very soluble in water and they are readily redistributed when cells are disrupted. Evidence suggests that a substantial proportion of the intracellular polyamines is attached to the ribosomes and that spermidine is not concentrated in the nucleus. 3. Polyamines bind strongly to both DNA and RNA. The strength of binding is:spermine > spermidine > putrescine. Polyamines stabilize the double helix of DNA, probably by forming a bridge across the narrow groove, by involving electrostatic bonding with the phosphate group. However, they do not appear to alter the overall conformation of DNA. Spermine enables single-stranded RNA to fold into a more compact configuration which is less susceptible to attack by ribonuclease. 4. Spermine and spermidine are able to stimulate the DNA primed RNA polymerase. They facilitate the removal of RNA from the DNA-RNA-enzyme complex. 5. Polyamines promote the association of ribosomal subunits and also the binding of amino acyl transfer RNA to ribosomes. They cause increased coding ambiguities in the process of translation in certain bacterial systems. 6. There is a close correlation between the intracellular concentration of spermidine and the rate of RNA synthesis both in rat liver and in Escherichia coli. Conditions which affect the rate of RNA synthesis also affect the concentration of free intracellular spermidine. 7. Bacteria usually contain putrescine and spermidine, whereas animal tissues contain spermine and spermidine. Spermidine probably fulfils the same role in both bacteria and animal tissues, but the presence of spermine, which is common to eucaryotes, is possibly associated with their more complex mechanisms for regulating RNA and protein synthesis. 相似文献
11.
Petropoulos AD Xaplanteri MA Dinos GP Wilson DN Kalpaxis DL 《The Journal of biological chemistry》2004,279(25):26518-26525
The effects of spermine on peptidyltransferase inhibition by an aminohexosylcytosine nucleoside, blasticidin S, and by a macrolide, spiramycin, were investigated in a model system derived from Escherichia coli, in which a peptide bond is formed between puromycin and AcPhe-tRNA bound at the P-site of poly(U)-programmed ribosomes. Kinetics revealed that blasticidin S, after a transient phase of interference with the A-site, is slowly accommodated near to the P-site so that peptide bond is still formed but with a lower catalytic rate constant. At high concentrations of blasticidin S (>10 x K(i)), a second drug molecule binds to a weaker binding site on ribosomes, and this may account for the onset of a subsequent mixed-noncompetitive inhibition phase. Spermine enhances the blasticidin S inhibitory effect by facilitating the drug accommodation to both sites. On the other hand, spiramycin (A) was found competing with puromycin for the A-site of AcPhe-tRNA.poly(U).70 S ribosomal complex (C) via a two-step mechanism, according to which the fast formation of the encounter complex CA is followed by a slow isomerization to a tighter complex, termed C(*)A. In contrast to that observed with blasticidin S, spermine reduced spiramycin potency by decreasing the formation and stability of complex C(*)A. Polyamine effects on drug binding were more pronounced when a mixture of spermine and spermidine was used, instead of spermine alone. Our kinetic results correlate well with cross-linking and crystallographic data and suggest that polyamines bound at the vicinity of the antibiotic binding pockets modulate diversely the interaction of these drugs with ribosomes. 相似文献
12.
The effects of potential inhibitors on the activity of neutral ribosomal proteinase--cathepsis R--were studied. It was found that cathepsin R belongs to the group of serine enzymes. The polyamines spermine and spermidine, which are inherently present in the ribosomes, are natural reversible inhibitors of cathepsin R. Upon separation of the enzyme from the inhibitors the proteinase displays a high activity. The effects of polyamines on the proteinase activity may either be direct or mediated via RNA. The enzyme activity can also be controlled by amino acids. Approximately 2/3 of cathepsis R were found in a latent state. 相似文献
13.
E. Gfeller D. N. Stern D. H. Russell C. C. Levy R. L. Taylor 《Cell and tissue research》1972,129(4):447-454
Summary Structural alterations of the nucleoli of rat liver cells were noted when these nuclei were isolated with spermidine or spermine rather than magnesium. When 5–10 mM spermidine or spermine were used to isolate the nuclei, the nucleoli were a) larger, b) contained numerous and sometimes large lacunae, and c) were less aggregated and had prominent chromatin caps. These chromatin caps gave the nucleolus a ring-shaped appearance in the light microscope. These findings, coupled with physiological data that indicate that polyamines enhance nucleolar RNA polymerase activity (Russell et al., 1971), suggest that spermidine and spermine may be involved in the control of ribosomal RNA synthesis. To our knowledge, this is the first instance of the direct stimulation of ribosomal RNA synthesis during nuclear isolation.Supported by USPHS Grant NS-07934. 相似文献
14.
The induced circular dichroism (CD) in the visible region of acridine orange bound to the double-stranded RNA from cytoplasmic polyhedrosis virus and to yeast tRNA has been measured as a function of RNA phosphate-to-dye ratio (P/D), under the conditions of 0.01 M Na+ at pH 7.0. The shape of the CD spectrum of acridine orange bound to the double-stranded RNA was quite different from the spectrum of the dye bound to DNA. The CD spectral features of acridine orange bound to the double-stranded regions in tRNA closely resembled those of the double-stranded RNA-dye complex, suggesting that the dyes bind similarly to the two RNA's. It was further found that the CD spectrum of the tRNA-dye complex at sufficiently high P/D ratios, which is assignable to monomeric, intercalated dye to the base-paired parts in tRNA, is also distinct from the corresponding spectrum of the DNA-dye complex. 相似文献
15.
Inhibition of bacterial growth by metal salts. The accumulation of ribonucleic acid during inhibition of Escherichia coli by cobalt chloride 总被引:10,自引:8,他引:2
During inhibition of the growth of Escherichia coli by cobalt chloride protein synthesis was decreased more than the synthesis of RNA. Three species of particle accumulated during the incubation. These had sedimentation coefficients of about 44s, 33s and 23s in tris buffer containing 10 mm-magnesium acetate and 100 mm-potassium chloride, but their sedimentation properties were susceptible to changes in buffer composition. The particles contained RNA but were more readily degraded by ribonuclease than were the ribosomes. RNA isolated from the particles differed slightly in sedimentation properties from the major species of ribosomal RNA. The particles are likely to be closely related to ribosome precursors that have been detected in other circumstances. Changes in the polyribosome fraction during inhibition by cobalt chloride, nickel chloride and chloramphenicol provided further evidence that inhibition by Co(2+) involves specific effects on the protein-synthesizing machinery. 相似文献
16.
Mobility of ribosomes bound to microsomal membranes. A freeze-etch and thin-section electron microscope study of the structure and fluidity of the rough endoplasmic reticulum 总被引:6,自引:4,他引:2
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《The Journal of cell biology》1977,72(3):530-551
The lateral mobility of ribosomes bound to rough endoplasmic reticulum (RER) membranes was demonstrated under experimental conditions. High- salt-washed rough microsomes were treated with pancreatic ribonuclease (RNase) to cleave the mRNA of bound polyribosomes and allow the movement of individual bound ribosomesmfreeze-etch and thin-section electron microscopy demonstrated that, when rough microsomes were treated with RNase at 4 degrees C and then maintained at this temperature until fixation, the bound ribosomes retained their homogeneous distribution on the microsomal surface. However, when RNase- treated rough microsomes were brought to 24 degrees C, a temperature above the thermotropic phase transition of the microsomal phospholipids, bound ribosomes were no longer distributed homogeneously but, instead, formed large, tightly packed aggregates on the microsomal surface. Bound polyribosomes could also be aggregated by treating rough microsomes with antibodies raised against large ribosomal subunit proteins. In these experiments, extensive cross-linking of ribosomes from adjacent microsomes also occurred, and large ribosome-free membrane areas were produced. Sedimentation analysis in sucrose density gradients demonstrated that the RNase treatment did not release bound ribosomes from the membranes; however, the aggregated ribosomes remain capable of peptide bond synthesis and were released by puromycin. It is proposed that the formation of ribosomal aggregates on the microsomal surface results from the lateral displacement of ribosomes along with their attached binding sites, nascent polypeptide chains, and other associated membrane proteins; The inhibition of ribosome mobility after maintaining rough microsomes at 4 degrees C after RNase, or antibody, treatment suggests that the ribosome binding sites are integral membrane proteins and that their mobility is controlled by the fluidity of the RER membrane. Examination of the hydrophobic interior of microsomal membranes by the freeze-fracture technique revealed the presence of homogeneously distributed 105-A intramembrane particles in control rough microsomes. However, aggregation of ribosomes by RNase, or their removal by treatment with puromycin, led to a redistribution of the particles into large aggregates on the cytoplasmic fracture face, leaving large particle-free regions. 相似文献
17.
Interaction between polyamines and nucleic acids or phospholipids 总被引:10,自引:0,他引:10
K Igarashi I Sakamoto N Goto K Kashiwagi R Honma S Hirose 《Archives of biochemistry and biophysics》1982,219(2):438-443
The binding of polyamines to DNA, RNA, and phospholipids has been studied by gel filtration and sucrose density gradient centrifugation. Spermine was found to bind more to a GC-rich DNA. Among RNAs containing double-stranded region [poly(AU), poly(GC), and ribosomal RNA], the binding of spermine was nearly equal. Among the single-stranded RNAs, the binding of spermine was in the order poly(U) > poly(C) > poly(A). An increase in K+ or Mg2+ concentration resulted in a great decrease in spermine binding to DNA and in a slight decrease in spermine binding to RNA. Therefore, in the presence of more than 2 mm Mg2+ and 100 mm K+, the binding of spermine to RNA was greater than that to DNA. No significant difference in spermine binding was observed between 16 S ribosomal RNA and 30 S ribosomal subunits, suggesting that ribosomal proteins did not affect significantly the binding of spermine to ribosomal RNA. The binding of spermine to microsomes was dependent on phospholipids. The binding strength was in the order phosphatidylinositol > phosphatidylethanolamine > phosphatidylcholine. 相似文献
18.
Ribosomal proteins and DNA-binding protein II from the extreme thermophile Bacillus caldolyticus 总被引:1,自引:0,他引:1
Crystallographic studies, presently on ribosomal and DNA-binding proteins from the moderate thermophile Bacillus stearothermophilus, can be expected to benefit from the use of even more stable proteins from extreme thermophiles. Bacillus caldolyticus, which is able to grow in the temperature range of 70-80 degrees C, appears to be a suitable candidate. We have compared the two bacilli using two criteria: the two-dimensional gel patterns of ribosomal proteins and the properties of DNA-binding protein II. The latter protein is ubiquitous in the eubacterial kingdom and can be purified in large quantities. B. caldolyticus can be grown at 75 degrees C in continuous culture with a generation time of 45-60 min. The yield of ribosomes compares favorably with that of B. stearothermophilus. The gel patterns of the ribosomal proteins are very similar but several differences, in particular among the 50S proteins, are observed. The N-terminal amino-acid sequence of the DNA-binding protein differs in 3 positions (out of 39) from B. stearothermophilus and the protein shows an increased resistance to thermal denaturation. Tetragonal and monoclinic crystals of DNA-binding protein II have been obtained which are suitable for X-ray studies and the diffraction patterns of the two crystal forms are shown. 相似文献
19.
A spectrophotometric study of the secondary structure of ribonucleic acid based on a method for diminishing single-stranded base-`stacking'' without affecting multihelical structures 总被引:1,自引:1,他引:0
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1. On the basis of studies with model compounds it was concluded that in 8m-urea-m-potassium chloride (or 4m-guanidinium chloride) in 0.01m-potassium phosphate buffer, pH7.0, multi-helical structures have about the same stability as in 0.1m-potassium phosphate buffer, pH7.0, whereas the tendency of base residues to ;stack' along a single polynucleotide chain is much decreased. 2. Base-pairing was eliminated whereas base-;stacking' persisted after RNA in 1% formaldehyde-0.1m-potassium phosphate buffer, pH7.0, was heated to 95 degrees . 3. From a study of the thermal denaturation of unfractionated transfer RNA from Escherichia coli and of RNA from the fractionated sub-units of rabbit reticulocyte ribosomes in 8m-urea-m-potassium chloride (or 4m-guanidinium chloride) in 0.01m-potassium phosphate buffer, pH7.0, it was inferred that ;stacked' residues may account for up to 25% of the increase in E(260) found on heating RNA in solvents such as 0.1m-potassium phosphate buffer, pH7.0. 4. Changes in the spectrum with temperature were analysed on the basis of the assumptions that (a) the polynucleotide chain is amorphous on denaturation (which is probable in 8m-urea-m-potassium chloride-0.01m-potassium phosphate buffer, pH7.0) and that (b) the polynucleotide chain adopts a single-stranded ;stacked' conformation on denaturation (which is probable when ordinary solvents such as 0.1m-potassium phosphate buffer, pH7.0, are used). 相似文献
20.
《Cell biology international reports》1983,7(11):955-962
The phenomenon of resistance of confluent 3T3 cells to serum stimulation of proliferation is investigated and shown to depend drastically on the kinetics of application of growth factors with the serum. The cellular content of ribosomal RNA is determined flow-cytometrically by measuring the red fluorescence of cells stained with acridine orange. Ribosomal RNA content of 3T3 cells, but not of SV40-3T3 cells, is shown to decrease after confluence. The kinetics of restoration of ribosomal RNA in stimulated 3T3 cells exhibits an increasing delay with increasing duration of quiescence. These and further results are consistent with “progression” to initiation of the cell cycle being closely associated with restoration of cellular content of ribosomes. 相似文献