Poly(A) sequences in plant polysomal RNA

Isolation and characterization of polysomes and polyadenylated polysomal RNA from Vicia faba meristematic root cells

Undegraded Vicia faba polysomes from meristematic root cells were obtained after homogenization in a medium of low ionic strength provided that the pH was equal to 9.0. By minimizing the shearing forces during the homogenization step, polysomes were obtained free of mitochondrial and nuclear contaminants, measured by differential spectrophotometry and CsCl gradient centrifugation respectively. Poly(A)-containing RNA was obtained by poly(U)-Sepharose chromatography and shown to be virtually free of rRNA and its average size was 13-15 S. Approximately 9% of the purified preparation was annealed by [3H]-poly(U). Sucrose gradient analysis under denaturing conditions showed that the poly(A)-CONtaining RNA were non-degraded. This RNA was used to direct the synthesis of proteins in a heterologous cell-free system from wheat germ.

RNA metabolism and membrane-bound polysomes in relation to globulin biosynthesis in cotyledons of developing field beans (Vicia faba L.)

In cotyledon cells of developing field beans the RNA content per cell does not change in the second half of developmental period 2, whereas globulin biosynthesis continues. The constant RNA content per cell results from an equilibrium between RNA synthesis and degradation. All types of RNA are synthesized until the end of globulin biosynthesis, but poly(A)-containing RNA was preferentially labelled during maximum globulin formation. During stage 2 of seed development of poly(A)-containing RNA fraction represents a discrete peak in the 12--18-S region on agarose gels and corresponds to the peak of poly(A)-containing RNA isolated from polysomes. alpha-Amanitin inhibits selectively the labelling of poly(A)-containing RNA and concomitantly globulin formation. Translation of total poly(A)-containing RNA, free and membrane-bound polysomes in a cell-free wheat germs demonstrates that the globulins are preferentially produced on membrane-bound polysomes and that poly(A)-containing RNA includes the mRNA for both vicilin and legumin.

Proteins bound to poly(A) sequences of polyribosomes from germinating wheat embryos

A preparation of purified polyribosomes was isolated from wheat embryos germinating for 1 h with [3H]adenosine. Treatment of polyribosomes with pancreatic ribonuclease leads to the liberation of particles containing poly(A) sequences. Poly(A)-containing complexes show a heterogeneous distribution in the region 8--15 S. The ability of 8--15 S material to be absorbed to membrane filters under the conditions of low ionic strength and its sensitivity to pronase indicate that poly(A) sequences in polyribosomes are associated with protein. Analysis of this protein by electrophoresis in a polyacrylamide gel demonstrates the presence of two polypeptides with the molecular weights equal to 86,000 and 52,000.

The polyadenylic sequences in the ribonucleic acid of the fern Anemia phyllitidis

The vegetative prothalli (1-3 weeks old) of Anemia were incubated for 24 h in [(14)C]adenine. The RNA was phenol extracted from whole cells and the poly (A) sequences were isolated by nuclease digestion followed by poly (U)-sepharose chromatography. About 2-3% of the total radioactivity was retained on the column. The base composition of the nuclease resistant RNA was: C, 1.4; G, 3.6; A, 93.3; and U, 1.7. It is concluded that Anemia RNA contains poly adenylate sequences.

Poly(A)-containing RNA in Tetrahymena pyriformis

Poly(A)-containing RNAs with sedimentation coefficients in the range 10-45 S and 10-35 S (Mr 0.2-3.3 x 10(6) and 0.2-2.2 x 10(6) approximately) are present in the nucleus and cytoplasm of T. pyriformis respectively. The poly(A) segments present in both nuclear and cytoplasmic poly(A)-containing RNAs have a chain length of 80 - 150 nucleotides. Significant amounts of high-molecular-weight poly(A)-containing RNAs (35 S, Mr 2.2 x 10(6) are found in the post-polysomal fraction of the cytoplasm (messenger ribonucleoprotein particles?) and also in large polysomes. In order to exclude the possibility that these high-molecular-weight species are products of non-specific aggregation, RNA preparations were submitted to severe denaturing conditions before analysis and all electrophoreses were carried out in the presence of 95% (v/v) formamide.

Preferential stimulation of the plant mRNA synthesis by gibberellic acid

1. Treatment of the etiolated maize seedlings with the plant hormone, gibberellic acid results in a significant enhancement of heavy polyribosome formation. 2. This is accompanied by highly increased incorporation of the labelled RNA precursors into RNA engaged in the polyribosomal complex, as well as by an increased rate of protein synthesis in vivo. 3. Determination of the specific radioactivity of particular RNA classes isolated from polyribosomes reveals that gibberellic acid stimulates mostly the synthesis of the rapidly labelled, non-ribosomal RNA fraction. 4. A considerable amount of this rapidly labelled RNA fraction, whose synthesis is preferentially stimulated by exogenous gibberellic acid contains poly(A) sequences, as shown by affinity chromatography on oligo (dT)-cellulose indicating that phytohormone causes an increased transcription of mRNA in etiolated maize seedlings. 5. When [3H]adenosine served as the RNA precursor it was found that the ratio between the heteropolymeric and polyadenylic parts of the poly(A)-RNA chain markedly changed under gibberellin treatment, suggesting that, in addition to an increased rate of mRNA synthesis, the plant hormone also affects the process of post-transcriptional polyadenylation of the newly made mRNA precursors. Possible extension of the polyadenylate segment in the presence of gibberellin may account for a longer functional half-life of the mRNA synthesized in plants treated with the phytohormone, and may explain significantly enhanced heavy polyribosome formation, as well as a higher efficiency of protein synthesis in plants treated with gibberellic acid.

Subcellular distribution and properties of poly(A)-containing RNA from cultured plant cells

Cultured sycamore cells rapidly incorporate [3H]uridine or [32P]orthophosphate into rRNA precursors and polydisperse RNA. Mature rRNA accumulates only after a lag period of approximately 40 min. Fractionation of pulse-labelled cells and analysis of the RNA shows that after 30 min the rRNA precursors, together with some polydisperse RNA, are confined to the nucleus. In consequence radioactive polydisperse RNA can be isolated from polyribosomes in the complete absence of labelled rRNA. Approximately 40% of this RNA is retained by an oligo(dT)-cellulose column and by this criterion is judged to contain poly(A) sequences. A smaller proportion of nuclear polydisperse RNA also contains poly(A). The tendency for poly(A)-containing RNA to aggregate complicates molecular weight determinations. Denaturation of poly(A)-containing RNA in 8 M urea prior to gel electrophoresis produces a broad peak of RNA with an average Mr = 10(6). Analysis of the nucleotide composition of total cell poly(A)-containing RNA shows that it contains 41% AMP. Roughly 6% of this RNA is resistant to digestion by ribonuclease A and T1. AMP is the only nucleotide detectable in these fragments. From their mobility during electrophoresis in 8 M urea at 60 degrees C with 5.8-S, 5-S and tRNA as molecular weight markers it is concluded that the poly(A) regions contain an average of 160 nucleotides.

[Studies on stable and during early imbibition phases synthesized poly(A)-RNA of Agrostemma githago embryos (author's transl)]

RNA isolated from dry embryos of Agrostemma githago seeds contains poly(A)-sequences, but in very small amounts. In the early phase of imbibition, an intensive synthesis of poly(A)-containing RNA is brought about. The importance of this synthesis of poly(A)-RNA is discussed.

The measurement of plant polyadenylic acid by hybridisation with radioactive polyuridylic acid

Saturation hybridisation of polyadenylic acid with [(3)H]polyuridylic acid is described. Under conditions of [(3)H]poly(U) excess, poly(A) is detected in the RNA of a number of higher plants. The ribonuclease resistant hybrids melt sharply when subjected to thermal denaturation. Plant RNA which contains poly(A) sequences detected by [(3)H]poly(U) hybridisation is polydisperse in molecular weight. Data presented shows that the amount of poly(A) in plant RNA is variable. This technique is useful for the qualitative and quantitative detection of poly(A) sequences in higher plant RNA.

Synthesis of polyadenylic acid-containing ribonucleic acid during the germination of Neurospora crassa conidia

Ribonucleic acid (RNA) synthesized during the first 1 h of conidial germination (15 to 20, 25 to 30, and 55 to 60 min) has been characterized by sucrose-sodium dodecyl sulfate gradient centrifugation, binding to polyuridylic acid filters, and oligo(dT)-cellulose chromatography. At all labeling periods examined, polyadenylic acid-containing RNA is synthesized, processed, and incorporated into polysomes. Approximately 40% of the labeled RNA sedimenting between 5 and 17S binds to polyuridylic acid filters. RNA which binds to oligo(dT)-cellulose displays a heterogeneous distribution in sucrose-sodium dodecyl sulfate gradients with a major, broad peak at 10-16S. In addition, some polyadenylic acid-containing RNA sediments beyond the 25S marker. Approximately 3% of the [3H]adenosine in pulse-labeled polysomal RNA is in polyadenylic acid segments resistant to pancreatic and T1 ribonucleases.

Polyadenylated RNA from Vicia faba meristematic root cells. Localization and size estimation of the poly (A) segment

After incubating root apices from two-day-old bean seedlings with [3H] adenine the RNA was extracted from whole cells or polysomes, and the poly (A) sequences were isolated by nuclease digestion followed by poly(U)-Sepharose chromatography. The alterations of the RNA molecules due to the various treatments were monitored by sucrose density gradients. It was found that sequential extraction first at pH 7.6 then at pH 9.0 did not result in a separation between RNA poor in poly(A) sequences and poly(A)-rich RNA. Furthermore chromatography analysis of hydrolysates from nuclease-resistant RNA extracted either at pH 7.6 or pH 9.0 revealed that AMP constituted nearly 95% of the bases and that the poly(A) sequences, about 200 bases, were located at the 3' terminus of the polyadenylated RNA. No size difference was found for the poly(A) segment between the pH-7.6-extracted RNA and that extracted at pH 9.0.

Synthesis and translation site of light-induced mRNAs in etiolated Euglena gracilis

Poly(a)-mRNA synthesis has been studied in etiolated Euglena gracilis exposed to 1 or 2 h of illumination. 1. Labeling kinetics of mRNAs containing poly(A) sequences, during illumination or after return to darkness, reach a plateau in 10 or 20 min according to nutritional conditions. When the cultures are returned to darkness, the mRNA synthesis decreases rapidly. Thus, the synthesis of these mRNAs (light-induced mRNAs) is dependent on light and their half-life can be evaluated. 2. Cycloheximide induces accumulation of label in poly(A)-containing mRNA; such an accumulation is not observed after addition of lincomycin. Labeling during illumination of mRNA in a chloroplast mutant is similar to that in the wild type strain. These data suggest that the poly(A)-mRNAs synthesized in the two first hours of illumination are translated on cytoplasmic polyribosomes.

Poly(A)-containing RNA from Petroselinum hortense: isolation, properties and messenger function in vitro

Cell suspension cultures from parsley (Petroselinum hortense Hoffm.) were labelled in vivo with [2-3H] adenosine. The RNA isolated from the ribosomal pellet was fractionated on an oligo(dT)-cellulose column. Approximately 1.5% of the RNA, representing about 15% of the total radioactivity, was retained at high salt concentrations and eluted at low ionic strength. As determined by two independent methods, this fraction contained poly(A) segments with an average length of about 80 nucleotides. It was active as template in a cell-free system from wheat germ, directing the synthesis of peptides ranging in molecular weight from about 4000-40000 daltons.

Messenger RNA metabolism of animal cells. Possible involvement of untranslated sequences and mRNA-associated proteins

The past several years have seen a virtual revolution in the study of eukaryotic mRNA. Among the notable recent achievements are the positive identification of mRNA precursors in HnRNA, the enumeration of the DNA sequences from which mRNA is transcribed, and the finding that mRNA in cultured cells is much more stable than was previously believed. One of most far-reaching discoveries has been the finding that mRNA in eukaryotes contains poly A. This discovery, aside from providing a powerful tool for mRNA isolation, has generated a large body of research into the properties and metabolism of poly A itself. In addition, the finding of a poly A-associated protein has given a renewed stimulus to the study of proteins associated with mRNA. This review is devoted to a discussion of these and related achievements, and some of their implications

Studies on messenger and ribosomal RNA synthesis in plant tissue cultures induced to undergo synchronus cell division

Messenger and ribosomal RNA metabolism was tudied in a plant tissue culture system: cells from the quiescent tubers of Helianthus tuberosus (Jerusalem artichoke) were induced to divide synchronously and dedeifferentiate by excision and culture of explants in nutrient medium. Large accumulations of ribosomal RNA and protein started early in the 20-h lag-period preceding the first division. In pulse-labelling experiments, two types of polydisperse messenger-like RNAs were detected one with and one without a poly(adenylic acid) sequence. In the first 2 h of culture the two polydisperse RNA fractions were the predominant types of RNA synthesised. Ribosomal RNA synthesis was very low during the first 2 h, but acclerated later. Low concentrations of actinomycin-D strongly inhibited ribosomal RNA synthesis, but had little effect on the synthesis of transfer RNA or either type of polydisperse messenger-like RNA. In explants cultured with low concentrations of actinomycin-D ribosomal RNA accumulation was completely inhibited, but cell division and protein accumulation occurred, though at a reduced rate. It is concluded that the synthesis and accumulation of new ribosomal RNA which normally occur during culture are not required for the induction of cell division or for protein accumulation, i.e. the ribosomal RNA existing in the quiescent tuver cells can support protein accumulation and cell division induced by excision and culture. The quiescent tuber tissue is also shown to contain significant amounts of messenger-like RNA.

The hybridisation of [(3)H]poly(uridylic) acid to DNA from Phaseolus aureus Roxb

[5-(3)H]poly(uridylic) acid hybridises to nuclear DNA, suggesting the DNA contains poly (deoxyadenylic) acid sequences. These regions do not appear to be clustered in the DNA. Although the amount of DNA involved is small it is sufficient for thousands of sequences. Thermal dissociation of the hybrids shows that a relatively small number of hydrogen bonds is involved in each and it is concluded that these sequences are relatively short. In view of the fact that much longer poly(adenylic) acid sequences are found in plant RNA it is concluded that these are added after transcription.

Gibberellic acid causes increased synthesis of RNA which contains poly(A) in barley aleurone tissue

Incubation of isolated barley aleurone layers with gibberellic acid for 16 hr caused a 50% increase in the synthesis of RNA that contains poly(A) sequences [poly(A)-RNA], but had no measurable effect on the syntheses of the major RNA species. The syntheses of both the poly(A) and the heteropolymeric fractions of the poly(A)-RNA were increased. The poly(A) sequences were separated into two classes by size, one containing an average of 250 nucleotides and the other about 70 nucleotides. The two classes occurred in a molar ratio of about 1:1. Gibberellic acid increased the syntheses of both sequences to the same extent. We interpret these results to mean that gibberellic acid increases specifically the synthesis of mRNA in this tissue.