Intranuclear Accumulation of Rna Resembling the Smaller Ribosomal Rna Component

1970 ◽  
Vol 6 (1) ◽  
pp. 53-72
Author(s):  
M. E. BRAMWELL
Keyword(s):  
Ribosomal Rna ◽  
Base Composition ◽  
Actinomycin D ◽  
Total Radioactivity ◽  
16S Ribosomal Rna ◽  
Low Concentrations ◽  
Rapid Accumulation ◽  
Nuclear Rna ◽  
Step Down ◽  
Nucleolar Rna

A study was made of the nuclear RNA in HeLa cells with particular reference to the rapidly labelled fractions. It was found that if cells were incubated at a high density, that is, under ‘step-down’ conditions, there was a rapid accumulation of RNA in the nucleus. The fraction of the nuclear RNA which includes rapidly labelled RNA and which binds tightly to columns of methylated albumin on kieselguhr increased in amount and reached levels which permitted enough of the material to be isolated for direct measurement of its base composition. This was found to be very similar to that of 16s ribosomal RNA. When cells growing logarithmically were treated with low concentrations of actinomycin D and then incubated in the presence of [3H]uridine it was found that an RNA fraction which bound tightly to methylated albumin on kieselguhr again accumulated in the nucleus. This fraction resembled that which accumulated under ‘step-down’ conditions. It contained over 85% of the total radioactivity in the nuclear RNA and again had a base composition very similar to 16s ribosomal RNA. Since nucleolar RNA synthesis was inhibited by the concentrations of actinomycin D used, it appeared that an RNA closely resembling 16s ribosomal RNA was synthesized outside the nucleolus. Sedimentation patterns on sucrose density gradients and thermal denaturation profiles lent support to the view that the RNA which binds tightly to columns of methylated albumin on kieselguhr probably represents ‘nascent’ 16s ribosomal RNA.

scholarly journals A study of nucleated erythrocytes by density-gradient centrifugation in a zonal rotor

1969 ◽  
Vol 111 (4) ◽  
pp. 583-591 ◽  
Author(s):  
A P Mathias ◽  
D. Ridge ◽  
N. St G. Trezona
Keyword(s):  
Molecular Weight ◽  
Ribosomal Rna ◽  
Base Composition ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Density Gradients ◽  
Avian Erythrocytes ◽  
Nuclear Rna ◽  
Zonal Rotor

1. Several substances of high molecular weight were examined for their suitability as suspension media in the formation of density gradients for the zonal centrifugation of avian erythrocytes. None proved satisfactory. 2. The behaviour of pigeon erythrocytes in rate-sedimentation experiments in a type A zonal rotor with density gradients of sucrose was examined. The mature cells sediment more rapidly than the younger cells and have a lower RNA/DNA ratio. Maturation is accompanied by a greater loss of RNA from the nucleus than from the cytoplasm. 3. The base composition of the nuclear RNA and of the two species of cytoplasmic ribosomal RNA is reported. 4. The RNA of erythrocytes may be labelled in vivo by injection of inorganic [32P]phosphate. The cells most active in the synthesis of RNA sediment less rapidly than the bulk of the cells. 5. Reticulocyte nuclei sediment more slowly than those from erythrocytes. Reticulocyte nuclei have a mean volume of 35μ3 and are isopycnic with sucrose of density 1·2871 (measured at 20°). Maturation of the nuclei causes them to shrink to a volume of 25μ3 and the density to increase to 1·2944.

Metabolism of high molecular weight, polydisperse, rapidly labeled nuclear RNA in rat liver

1968 ◽  
Vol 46 (12) ◽  
pp. 1497-1505 ◽  
Author(s):  
Maurice Brossard ◽  
Louis Nicole
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Rat Liver ◽  
Ribosomal Rna ◽  
Base Composition ◽  
Orotic Acid ◽  
Chromosomal Origin ◽  
Base Analysis ◽  
Nuclear Rna ◽  
Kinetics Of

Studies of the metabolism of rat liver RNA showed the existence of two species of rapidly labeled nuclear RNA: a 45 S preribosomal type of nucleolar origin, and a 6–50 S polydisperse RNA of chromosomal origin. The kinetics of labeling with orotic acid-14C and the nature of the latter RNA have been investigated. The following findings are reported, (1) This RNA is composed of at least four main classes of RNA having sedimentation coefficients of approximately 45, 35, 24, and 18 S. (2) Except for the 18 S class which seems to be an end product, the three other classes have a rapid turnover and do not appear to leave the nucleus. (3) Base analysis after 32P incorporation indicates that these four classes of RNA have a similar base composition with a G+C/A + U ratio in the range of 0.98–1.07, which resembles DNA more closely than ribosomal RNA. (4) The 6–50 S polydisperse RNA has a different metabolism than that of the 45 S preribosomal type and there is no precursor-to-product relationship between these two species of RNA.

scholarly journals THE SELECTIVE INTERRUPTION OF NUCLEOLAR RNA SYNTHESIS IN HELA CELLS BY CORDYCEPIN

1969 ◽  
Vol 41 (2) ◽  
pp. 510-520 ◽  
Author(s):  
Moshe Siev ◽  
Robert Weinberg ◽  
Sheldon Penman
Keyword(s):  
Ribosomal Rna ◽  
Hela Cells ◽  
Rna Synthesis ◽  
Transfer Rna ◽  
Short Exposure ◽  
Low Concentrations ◽  
Dna And Protein Synthesis ◽  
Ribosomal Precursor ◽  
Precursor Molecules ◽  
Nucleolar Rna

Cordycepin is an analogue of adenosine lacking the 3'-OH. When incorporated into a growing RNA molecule, cordycepin prevents further elongation, thus producing a prematurely terminated RNA molecule. When HeLa cells are exposed to low concentrations of cordycepin, DNA and protein synthesis are unaffected during short exposure periods. The synthesis of completed ribosomal and ribosomal-precursor (45S) RNA is significantly depressed. Partially completed 45S ribosomal precursor molecules accumulate in the nucleolus. 18S ribosomal RNA can be cleaved from these incomplete precursors, while 32S ribosomal precursor cannot be produced from partially snythesized 45S molecules. The synthesis of transfer RNA is also reduced in the presence of cordycepin. The synthesis of the nuclear heterogeneous RNA species is unaffected by the drug while the cytoplasmic heterogeneous RNA is slightly reduced.

scholarly journals The behaviour of heterogeneous nuclear ribonucleic acid in partially and completely denaturing conditions

1974 ◽  
Vol 141 (2) ◽  
pp. 477-484 ◽  
Author(s):  
Michael E. Bramwell
Keyword(s):  
Molecular Weight ◽  
Ionic Strength ◽  
High Temperatures ◽  
Sedimentation Rate ◽  
Ribonucleic Acid ◽  
28S Rrna ◽  
Nuclear Rna ◽  
Step Down ◽  
Low Ionic Strength ◽  
Nucleolar Rna

It is shown that the heterogeneous nuclear RNA (HnRNA) synthesized in the presence of actinomycin and at low and high temperatures sediments in low-ionic-strength sucrose gradients between the rRNA components, similar to the unmethylated RNA synthesized under ‘step-down’ conditions. If the ionic strength is increased then the HnRNA sediments more rapidly than 28S rRNA, with a large proportion about the 45S precursor rRNA position. Initially this was thought to be due to aggregation of the HnRNA; however, centrifugation and electrophoresis in completely denaturing conditions suggest that the molecular weight of this species of RNA is very large The experiments reveal that HnRNA is conformationally unstable relative to the nucleolar RNA and that the slower sedimentation rate of HnRNA in 5mm-EDTA–Tris base–sucrose gradients reflects the greater expansion of the HnRNA relative to the nucleolar RNA. The implications of this finding are discussed.

scholarly journals U3 small nuclear RNA can be psoralen-cross-linked in vivo to the 5' external transcribed spacer of pre-ribosomal-RNA

1989 ◽  
Vol 86 (17) ◽  
pp. 6523-6527 ◽  
Author(s):  
R L Maser ◽  
J P Calvet
Keyword(s):  
Ribosomal Rna ◽  
Ribosome Biogenesis ◽  
Rrna Processing ◽  
Small Nuclear Rna ◽  
Early Cleavage ◽  
External Transcribed Spacer ◽  
Nuclear Rna ◽  
Processing Event ◽  
Nucleolar Rna

U3 small nuclear RNA is hydrogen-bonded to high molecular weight nucleolar RNA and can be isolated from greater than 60S pre-ribosomal ribonucleoprotein particles, suggesting that it is involved in processing of ribosomal RNA precursors (pre-rRNA) or in ribosome biogenesis. Here we have used in vivo psoralen cross-linking to identify the region of pre-rRNA interacting with U3 RNA. Quantitative hybridization selection/depletion experiments with clones of rRNA-encoding DNA (rDNA) and cross-linked nuclear RNA showed that all of the cross-linked U3 RNA was associated with a region that includes the external transcribed spacer (ETS) at the 5' end of the human rRNA precursor. To further identify the site of interaction within the approximately 3.7-kilobase ETS, Southern blots of rDNA clones were sandwich-hybridized with cross-linked RNA and then probed for cross-linked U3 RNA. These experiments showed that U3 RNA was cross-linked to a 258-base sequence between nucleotides +438 and +695, just downstream of the ETS early cleavage site (+414). The localization of U3 to this region of the rRNA precursor was not expected from previous models for a base-paired U3-rRNA interaction and suggests that U3 plays a role in the initial pre-rRNA processing event.

Synthese und Umsatz von Ribonucleinsäuren in suspendierten Säugetierzellen

1966 ◽  
Vol 21 (10) ◽  
pp. 967-971 ◽  
Author(s):  
G. Koch ◽  
G. Trams ◽  
H. Kubinski
Keyword(s):  
Ribosomal Rna ◽  
Messenger Rna ◽  
Mammalian Cells ◽  
Base Composition ◽  
Low Concentrations ◽  
Dose Dependent

Actinomycin shows four effects on the synthesis and turnover of RNA in mammalian cells: in inhibits the synthesis of cellular RNA, it influences the base composition of newly synthesized RNA, it induces the degradation of a certain fraction of preformed RNA and it prevents the turnover of RNA synthesized in the presence of actinomycin. The first three activities are dose dependent. Synthesis of ribosomal RNA is inhibited by very low concentrations of actinomycin (0,005 μg/ml) whereby synthesis of messenger RNA continues.

scholarly journals A functional pseudoknot in 16S ribosomal RNA.

1991 ◽  
Vol 10 (8) ◽  
pp. 2203-2214 ◽  
Author(s):  
T. Powers ◽  
H.F. Noller
Keyword(s):  
Ribosomal Rna ◽  
16S Ribosomal Rna
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