Regulation of poly(A) polymerase activity and poly(A)+ RNA in germinated wheat embryos under conditions of pathogenesis

The induction of poly(A) polymerase was accompanied by a rise in the level of poly(A)⁺ RNA during early germination of excised wheat embryos (48 h). Fractionation of this RNA-processing enzyme by acrylamide gel electrophoresis and also by molecular sieving on Sephadex G-200 revealed a single molecular form of poly(A) polymerase with a molecular weight of 125 000. Wheat poly(A) polymerase specifically catalyzed the incorporation of [³H]AMP from [³H]ATP into the polyadenylate product only in the presence of primer RNA. Substitution of [³H]ATP by other labelled nucleoside triphosphates, such as [³H]GTP, [³H]UTP or [α-³²P]CTP in the assay mixture did not yield any labelled polynucleotide reaction product. The ³H-labelled reaction product was retained on poly(U)-cellulose affinity column and was not degraded by RNAase A and RNAase T₁ treatment. In addition, the nearest-neighbour frequency analysis of the ³²P-labelled reaction product predominantly yielded [³²P]AMP. Thus, characterization of the reaction product clearly indicated its polyadenylate nature. The average chain length of the [³H]poly(A) product was 26 nucleotides. Infection of germinating wheat embryos by a fungal pathogen (Drechslera sorokiana) brought about a severe inhibition (62–79%) of poly(A) polymerase activity. Concurrently, there was a parallel decrease (73%) in the level of poly(A)⁺ RNA. Inhibition of poly(A) polymerase activity in infected embryos could be due to enzyme inactivation, which in turn brought about a downward shift in the level of poly(A)⁺ RNA. The crude extract of the cultured pathogen contains a non-dialysable, heat-labile factor, which, along with a ligand, inactivates (65–74%) poly(A) polymerase in vitro. The fungal extracts also contained a dialysable, heat-stable stimulatory effector which activated wheat poly(A) polymerase (3.6–4.0-fold stimulation) in vitro. However, the stimulatory fungal effector was not expressed in vivo, but was detectable after the inhibitory fungal factor had been destroyed by heat-treatment in our in vitro experiments.     

Electrophoretic analysis of newly synthesized and stored maternal RNA during oogenesis ofCalliphora erythrocephala (Dipt.)

Summary Ovaries ofC. erythrocephala synthesize large amounts of poly(A)⁺ and poly(A)^– RNA during early and middle stages of oogenesis as shown by labelling with³H-uridine in vivo. After incubation for 1 h, a striking difference in the electrophoretic pattern of newly synthesized labelled poly(A)⁺ RNA and the poly(A)⁺ RNA present in sufficient amounts for optical density measurements (steady state poly(A)⁺ RNA) was observed. During early and mid-oogenesis, in the poly(A)^– RNA fraction, 4S predominantly mature rRNA, 5S RNA and tRNA were labelled. These fractions were no longer synthesized during late oogenesis, whereas poly(A)⁺ RNA was labelled continously During oogenesis stage specific differences in the size distribution of newly synthesized and steady state poly(A)⁺ RNA were not obvious. However, different sizes of labelled poly(A)⁺ RNA species were detected in 0–2h old preblastoderm embryos, after injection of³H-uridine into females either 3–4 days (stage 3–4 of oogenesis) or 24 h before oviposition (stage 5–6 of oogenesis). This difference in RNA synthesis was related to the presence of active nurse cell nuclei. The poly(A)⁺ RNA fraction represents about 2–3% of the total RNA in both ovaries and freshly laid eggs as judged by measurements of optical density and radioactivity bound to oligo(dT). The length of poly(A)-segments in ovarian poly(A)⁺ RNA varied from about 30 to 200 nucleotides.     

CHARACTERIZATION OF POLY(A) SEQUENCES IN BRAIN RNA

—Nuclear and polysomal brain RNA from the rabbit bind to Millipore filters and oligo(dT)-cellulose suggesting the presence of poly(A) sequences. The residual polynucleotide produced after RNase digestion of ³²P pulse-labelled brain RNA is 95% adenylic acid and 200-250 nucleotides in length. After longer isotope pulses the polysomal poly(A) sequence appears heterodisperse in size and shorter than the nuclear poly (A). Poly(A) sequences of brain RNA are located at the 3′-OH termini as determined by the periodate-[³H]NaBH₄ labelling technique. Cordycepin interferes with the processing of brain mRNA as it inhibits in vivo poly(A) synthesis by about 80% and decreases the appearance of rapidly labelled RNA in polysomes by about 45%. A small poly(A) molecule 10-30 nucleotides in length is present in rapidly labelled RNA. It appears to be less sensitive to cordycepin than the larger poly(A) and is not found in polysomal RNA.     

Double-stranded RNA specific nuclease from germinating embryos ofPennisetum typhoides

A double-stranded RNA specific nuclease (ds RNase) has been purified from the pearl milletPennisetum typhoides. The purification involved S-30 preparation from the germinating embryos, DEAE-cellulose and DNA-cellulose chromatography. The partially pure enzyme preferentially solubilized the synthetic double-stranded polynucleotide [³H]poly(rA) · poly(rU); the degradation of [³H]poly(rC) was fourteen fold lower under the same assay conditions. Further more, the ds RNase activity was inhibited to an extent of 58% by ethidium bromide, which is known to intercalate with double-stranded RNAs. Active sulfhydryl groups were found to be necessary for the ds RNase activity since the enzyme action was inhibited by N-ethylmaleimide. Ethidium bromide and N-ethyl-maleimide did not significantly inhibit the ss RNase activity. In contrast, diethyl pyrocarbonate inhibited ss RNase activity completely and ds RNase by 58%. Heating the enzyme for 20 min at 50°C resulted in drastic loss of both enzyme activities. The ds RNase showed maximum activity in the pH range of 6.5 to 7.5. The enzyme actsin vitro onE. coli 30S precursor ribosomal RNA and the cleavage products migrated in the region of mature 23S and 16S rRNAs.     

Intracellular levels of polyadenylated RNA and loss of vigour in germinating wheat embryos

Polyadenylated-RNA (Poly(A)⁺RNA) levels have been studied during the germination of wheat embryos of high viability but differing vigour. In high-vigour embryos imbibed at 20°C the level of poly(A)⁺RNA falls dramatically over the first hour of imbibition, then remains constant up to 3 h of imbibition before increasing rapidly to a level similar to that found in the quiescent state by 7 h of imbibition. Median-vigour embryos imbibed at 20°C show similar changes in poly(A)⁺RNA content but the initial decrease and subsequent increase in poly(A)⁺RNA levels are less marked. On imbibition at 10°C, the poly(A)⁺RNA content in high-vigour embryos decreases to a lesser extent during the first hour than at 20°C and the level increases more slowly over the next 6 h than during the same time period at 20°C. The level of poly(A)⁺RNA in medianvigour embryos remains constant over the first 4 h of germination and then falls to a level of about half that found in quiescent high-vigour embryos. Polyacrylamide gel electrophoresis of total-RNA samples shows that the polyadenylic acid (poly(A)) sequences occur in RNA species ranging in size from 35-7S. Polyacrylamide gel electrophoresis of isolated poly(A) sequences demonstrates the presence of two size classes of poly(A) in quiescent embryos, but at 20°C a more heterodisperse pattern appears by 2 h of imbibition. At 10°C, two size classes of poly(A) persist throughout the period studied in both high- and median-vigour embryos, although in median-vigour embryos the ratio of larger: smaller poly(A)-tail sizes decreases more rapidly than in high-vigour embryos.Abbreviations Poly(A) polyadenylic acid - poly(U) polyuridylic acid - poly(A)⁺RNA polyadenylated RNA     

Biochemical characterization of the RNA-hydrolytic activity of a pumpkin 2S albumin

A pumpkin 2S albumin with ribonuclease (RNase) activity was purified from pumpkin seeds (Cucurbita sp.) by liquid chromatographic techniques. It manifested potent RNase activity toward baker’s yeast RNA and calf liver RNA, and some polyhomoribonucleotides, including poly(A), poly(U) and poly(C) but not poly(G). Moreover, it was able to hydrolyze total RNA of both animal and plant origins. Ions such as Na⁺, Mg²⁺, Ca²⁺, and Zn²⁺ inhibited its RNase activity. Since RNase activity has not been previously reported in 2S albumins, this work may shed further light on the biological importance of this group of proteins.     

Messenger RNA for isocitrate lyase from Chlorella fusca var. vacuolata

Chlorella fusca cultures growing in the light and adapting to acetate in the dark were labelled with adenine-³H and adenine-¹⁴C, respectively. Poly(A)-containing RNA from the mixed cultures was analysed for ¹⁴C/³H ratio after polyacrylamide gel electrophoresis in 98% formamide. The RNA from acetateadapting C. fusca cells contained excess label migrating in the gels at a position equivalent to about 0.85×10⁶ mol.wt. Partially purified anti-isocitrate lyase serum linked to p-aminobenzoyl-cellulose bound 3.5–13% of polysomes from acetate-adapting C. fusca, containing 5–10% of polysomal poly(A)-containing RNA. The antibody-bound poly(A)-containing RNA fraction showed a unimodal size distribution with a mean size of about 0.85×10⁶ mol.wt. after electrophoresis on 4% polyacrylamide gels in 98% formamide. Cell-free translation assays showed a three-fold enrichment of isocitrate lyase mRNA after antibody selection of polysomes and indicated that isocitrate lyase mRNA was abundant in acetate-adapting C. fusca cells.Abbreviations A ₂₆₀ unit The amount of material in 1.0 ml giving an absorbance of 1.0 at 260 nm in a 1 cm light path - PAB-cellulose p-aminobenzoyl-cellulose - SDS sodium lauryl sulphate To whom offprint requests are to be sent     

The nucleotide sequence at the 5'' end of foot and mouth disease virus RNA.

Foot and mouth disease virus RNA has been treated with RNase H in the presence of oligo (dG) specifically to digest the poly(C) tract which lies near the 5' end of the molecule (10). The short (S) fragment containing the 5' end of the RNA was separated from the remainder of the RNA (L fragment) by gel electrophoresis. RNA ligase mediated labelling of the 3' end of S fragment showed that the RNase H digestion gave rise to molecules that differed only in the number of cytidylic acid residues remaining at their 3' ends and did not leave the unique 3' end necessary for fast sequence analysis. As the 5' end of S fragment prepared form virus RNA is blocked by VPg, S fragment was prepared from virus specific messenger RNA which does not contain this protein. This RNA was labelled at the 5' end using polynucleotide kinase and the sequence of 70 nucleotides at the 5' end determined by partial enzyme digestion sequencing on polyacrylamide gels. Some of this sequence was confirmed from an analysis of the oligonucleotides derived by RNase T1 digestion of S fragment. The sequence obtained indicates that there is a stable hairpin loop at the 5' terminus of the RNA before an initiation codon 33 nucleotides from the 5' end. In addition, the RNase T1 analysis suggests that there are short repeated sequences in S fragment and that an eleven nucleotide inverted complementary repeat of a sequence near the 3' end of the RNA is present at the junction of S fragment and the poly(C) tract.     

Endonucleolytic cleavage of murine leukemia virus 35S RNA by microsome-associated nuclease.

Moloney murine leukemia virus 35S RNA (molecular weight 3 to 3.4 × 10⁶) is cleaved by nuclease activity present in microsomal fractions from MLV infected or uninfected mouse embryo cells to two RNA species of approximate molecular weights 1.8 × 10⁶ and 1.5 × 10⁶. Microsomal fractions from MLV infected and uninfected cells also contained nucleolytic activity that solubilized [³H]poly(A)·poly(U) but not [³H]poly(C) or [³H]poly(U); the cleavage of poly(A)·poly(U) was inhibited by ethidium bromide. The cleavage of MLV RNA was also inhibited by ethidium bromide, suggesting double stranded regions in 35S RNA as the site of cleavage.     

Vorstufen der ribosomalen RNA in frei suspendierten Calluszellen der Petersilie (Petroselinum sativum)

Summary Six high molecular weight, rapidly labelled RNA species were detected in freely suspended callus cells of Petroselinum sativum by means of isotope labelling and electrophoretic separation in agarose-polyacrylamide gels. On the basis of their migration in the latter the RNA species were calculated to have the following molecular weights: 2.9×10⁶, 2,4×10⁶, 1.9×10⁶, 1.4×10⁶, 1.0×10⁶ and 0.75×10⁶ daltons. Thus they can clearly be distinguished from the two ribosomal RNA species (1.3×10⁶ and 0.7×10⁶ daltons). During incubation of the cells with [³H]methyl-methionine as a methyl donator all six components incorporated radioactivity rapidly. With [³H]nucleosides or [³H]orotic acid as precursors the 2.9×10⁶ and the 2.4×10⁶ daltons RNA were labelled within 10 min, while the other high molecular weight species appeared after about 20 min of labelling.Prolongation to 45–120 min resulted in accumulation of radioactivity preferentially in the 1.4×10⁶ and 0.75×10⁶ daltons RNA and in the ribosomal RNA species. The results of cell fractionation experiments provide evidence that these rapidly labelled high molecular weight RNA species are synthesized in the cell nucleus. The kinetics of their synthesis together with the other data obtained strongly support the suggestion that these RNA species function as precursors in the processing of ribosomal RNA. The possible mechanism of this process is discussed.

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Verwendete Abkürzungen EDTA Äthylendiamintetraessigsäure - DNase Desoxyribonuclease - Imp./min epm - MAK methyliertes Albumin an Kieselgur - POPOP 1,4- bis (4-Methyl-5-Phenyloxazol)-Benzol - PPO 2,5-Diphenyloxazol - RNase Ribonuclease - S Sedimentationskoeffizient in Svedberg-Einheiten - SDS Natriumdodecylsulfat - TPE Tris-Phosphat-EDTA-Puffer - Tris Tris-(hydroxymethyl)-aminomethan - Upm rpm     

The putative 15 S precursor of globin mRNA contains a poly(A) sequence

[³H]Uridine or [³H]adenosine pulse-labelled nuclear RNA was isolated from chicken immature red blood cells and separated on denaturing formamide sucrose gradients. RNA of each gradient fraction was hybridized with unlabelled globin DNA complementary to mRNA (cDNA) and subsequently digested by RNAase A and RNAase T₁. The experiments revealed two RNA species with globin coding sequences sedimenting at 9 S and approx. 15 S, the latter probably representing a precursor of 9 S globin mRNA.A poly(A) sequence was demonstrated in this RNA by two different approaches. Nuclear RNA pulse-labelled with [³H]uridine was fractionated by chromatography on poly(U)-Sepharose. Part of the 15 S precursor was found in the poly(A)-containing RNA. In the second approach 15 S RNA pulse-labelled with [³H]adenosine was hybridized with globin cDNA, incubated with RNAase A and RNAase T₁ and subjected to chromatography on hydroxyapatite. The hybrids were isolated and after separation of the strands degraded with DNAase I, RNAase A and RNAase T₁. By this procedure poly(A) sequences of approximately 100 nucleotides could be isolated from the 15 S RNA with globin coding sequences. The poly(A) sequence was completely degraded by RNAase T₂.     

rnr gene from the antarctic bacterium Pseudomonas syringae Lz4W, encoding a psychrophilic RNase R

RNase R is a highly processive, hydrolytic 3′-5′ exoribonuclease belonging to the RNB/RNR superfamily which plays significant roles in RNA metabolism in bacteria. The enzyme was observed to be essential for growth of the psychrophilic Antarctic bacterium Pseudomonas syringae Lz4W at a low temperature. We present results here pertaining to the biochemical properties of RNase R and the RNase R-encoding gene (rnr) locus from this bacterium. By cloning and expressing a His₆-tagged form of the P. syringae RNase R (RNase R^Ps), we show that the enzyme is active at 0 to 4°C but exhibits optimum activity at ∼25°C. The enzyme is heat labile in nature, losing activity upon incubation at 37°C and above, a hallmark of many psychrophilic enzymes. The enzyme requires divalent cations (Mg²⁺ and Mn²⁺) for activity, and the activity is higher in 50 to 150 mM KCl when it largely remains as a monomer. On synthetic substrates, RNase R^Ps exhibited maximum activity on poly(A) and poly(U) in preference over poly(G) and poly(C). The enzyme also degraded structured malE-malF RNA substrates. Analysis of the cleavage products shows that the enzyme, apart from releasing 5′-nucleotide monophosphates by the processive exoribonuclease activity, produces four-nucleotide end products, as opposed to two-nucleotide products, of RNA chain by Escherichia coli RNase R. Interestingly, three ribonucleotides (ATP, GTP, and CTP) inhibited the activity of RNase R^Ps in vitro. The ability of the nonhydrolyzable ATP-γS to inhibit RNase R^Ps activity suggests that nucleotide hydrolysis is not required for inhibition. This is the first report on the biochemical property of a psychrophilic RNase R from any bacterium.     

Multiple oligo(A) tracts associated with inactive sea urchin maternal mRNA sequences

Maternal RNA of sea urchin eggs and embryos was analyzed for short poly(A) sequences by digesting hybrids formed between [³H]poly(U) and poly(A) with RNase at 4°C. When the undigested [³H]poly(U) is precipitated with CTAB, all (A)_n tracts longer than 6 nucleotides are detected. This assay revealed a poly(A) content severalfold higher than is obtained with a similar assay using RNase at higher temperatures. On polyacrylamide gel electrophoresis, most of the previously undetected (A)_n tracts ran as a peak of oligo(A) of less than 20 nucleotides which accumulated at the dye front. The oligo(A) sequences were resolved into a single peak of (A)₁₀ when sized on Sephadex G100. These (A)₁₀ sequences were associated with large mRNA-sized molecules of about 3000 nucloetides average length which comprised 0.5 to 2% of the total maternal RNA. However, the (A)₁₀ sequences were not in mRNA molecules containing 3′-terminal poly(A) of 50–120 nucleotides nor did they remain in RNA that entered polysomes upon fertilization. However, hybridization studies showed that all sequences represented in the maternal poly(A)-containing RNA appeared to be present in the RNA molecules containing only (A)₁₀ sequences. The results suggest that the (A)₁₀-containing RNA might be incompletely processed mRNA precursor-like molecules.     

The presence of polyriboadenylic acid sequences in calf lens messenger RNA

The presence of poly(rA) sequences in lens RNA has been demonstrated by the isolation of RNase A and T₁-resistant fragments of approximately 50 nucleotide residues. These poly(rA)-rich sequences, obtained from lenses incubated for six hours in organ culture with [³H]adenosine, are located at the 3′ termini of mRNA as determined by 3′ exoribonuclease digestion. Limited digestion of the [³H]adenosine-labeled mRNA with the enzyme led to the abolition of binding to poly(rU)-filters and a concomitant loss of template activity with avian myeloblastosis virus RNA-dependent DNA polymerase. Furthermore, after incubation of lenses in organ culture with 3′-deoxyadenosine, the isolated polysomal RNA was unable to function as a template in an avian myeloblastosis virus RNA-dependent DNA polymerase-catalyzed reaction system.     

Analysis of the membrane-associated poly(A)+RNA in the cytoplasm of dormant Artemia cysts by DNA excess hybridization: Evidence for a nuclear origin

Encysted embryos of Artemia contain latent mRNA, to a large extent associated with a fraction of cytoplasmic membranes. The membranes, purified by EDTA treatment and banding in a sucrose gradient at 1.17 g/cm³, include endoplasmic vesicles and mitochondria. The origin of the membrane-associated poly(A)⁺RNA was therefore investigated. In gel electrophoresis poly(A)⁺RNA from the purified membranes of dormant cysts forms two distinct bands at approx. 3·10⁵ and 5·10⁵ Da. Later during development the lighter component decreases. Nuclei from dormant cysts are devoid of poly(A)⁺RNA, while nuclei from developing embryos (50% emergence) contain a predominant poly(A)⁺RNA component of approx. 5·10⁵ Da. ¹²⁵I-labelled preparations of nuclear DNA and of nuclear and membrane-associated poly(A)⁺RNA were used in reassociation and hybridization experiments with excess nuclear DNA. Poly(A)⁺RNA from the membranes of dormant cysts hybridized to nuclear DNA to the same extent as the nuclear poly(A)⁺RNA from developing embryos. The hybridization of labelled, nuclear poly(A)⁺RNA to nuclear DNA was strongly inhibited by unlabelled membrane RNA from either dormant cysts or developing embryos. It is concluded that the stored, membrane-associated poly(A)⁺RNA in dormant cysts is essentially of nuclear origin. The 5·10⁵-Da component is largely homologous with the corresponding component of nuclear poly(A)⁺RNA at later stages.     

Covalent attachment of poly (U) template to 40S - mammalian ribosomal subunits

When 40S subunits are irradiated at 254nm in presence of [³H] poly (U), formation of a 40S subunit-poly (U) complex can be demonstrated either by filtration technique at low Mg⁺⁺ concentration or by polyacrylamide gel electrophoresis. No stable complex was detected using unirradiated samples under the same conditions. Electrophoresis of this complex in the presence of dodecyl sulfate showed that part of the poly (U) directly associates with 18S RNA. This association is not through proteins, since it is not disrupted by pronase treatment.     

Ethylenediamine derivatives efficiently react with oxidized RNA 3′ ends providing access to mono and dually labelled RNA probes for enzymatic assays and in vivo translation

Development of RNA-based technologies relies on the ability to detect, manipulate, and modify RNA. Efficient, selective and scalable covalent modification of long RNA molecules remains a challenge. We report a chemical method for modification of RNA 3′-end based on previously unrecognized superior reactivity of N-substituted ethylenediamines in reductive amination of periodate-oxidized RNA. Using this method, we obtained fluorescently labelled or biotinylated RNAs varying in length (from 3 to 2000 nt) and carrying different 5′ ends (including m⁷G cap) in high yields (70–100% by HPLC). The method is scalable (up to sub-milligrams of mRNA) and combined with label-facilitated HPLC purification yields highly homogeneous products. The combination of 3′-end labelling with 5′-end labelling by strain-promoted azide-alkyne cycloaddition (SPAAC) afforded a one-pot protocol for site-specific RNA bifunctionalization, providing access to two-colour fluorescent RNA probes. These probes exhibited fluorescence resonance energy transfer (FRET), which enabled real-time monitoring of several RNA hydrolase activities (RNase A, RNase T1, RNase R, Dcp1/2, and RNase H). Dually labelled mRNAs were efficiently translated in cultured cells and in zebrafish embryos, which combined with their detectability by fluorescent methods and scalability of the synthesis, opens new avenues for the investigation of mRNA metabolism and the fate of mRNA-based therapeutics.     

Isolation and identification of mRNA for the high-molecular-weight storage proteins of wheat endosperm

The prolamin storage proteins of the wheat endosperm contain a sub-class of high-molecular-weight (HMW) polypeptides which have been implicated in determining breadmaking quality. Membrane-bound polysomes isolated from developing wheat endosperms contain mRNA for these HMW components. Although unfractionated polyadenylated RNA derived from the polysomes did not direct the synthesis of these components in an in-vitro wheat-germ system, it did when incubated with a rabbit reticulocyte lysate system. Identification of the translation products as HMW prolamins was based on their large incorporation of [³H]leucine and [³H]glycine relative to [³H]lysine, their mobility on polyacrylamide-gel electrophoresis and the observation that the changes of mobility in response to change in wheat genotype were the same as those observed for the authentic protein. The mRNA was fractionated by electrophoresis and density-gradient centrifugation. The mRNA for the HMW prolamins was found to have a relative molecular mass of about 1.6·10⁶.Abbreviations HMW high molecular weight - PAGE polyacrylamide-gel electrophoresis - poly(A)⁺RNA polyadenylated RNA - SDS sodium dodecyl sulphate     

Cloning of cDNA sequences derived from poly(A)+ nuclear RNA ofXenopus laevis at different developmental stages: Evidence for stage specific regulation

Summary Nuclear poly(A)⁺ RNA was isolated from gastrula and early tadpole stages ofXenopus laevis, transcribed into cDNA and integrated as double stranded cDNA by the G-C joining method into the Pst cleavage site of plasmid pBR 322. After cloning inE. coli strain HB 101 the clone libraries were hybridized to³²P labelled cDNA derived from nuclear poly(A)⁺ RNA of the two different developmental stages. About 20% of the clones gave a positive hybridization signal thus representing RNA molecules of high and medium abundance. From these clones, some individual clones were identified containing sequences which are not present at the oocyte and gastrula stages but which are transcribed at the early tadpole stage of embryonic development.     

Microspectrophotometric determination of the relative contents of nucleic acids in Pinus silvestris pollen

Based on inhibitor studies it has been concluded that in photoregulated processes of plant development, light induces differential gene expression. Using affinity chromatography of double labelled polysomal RNA on poly(U)-sepharose 4B, we were able to demonstrate different ³H/¹⁴C ratios for the bound poly(A) containing fraction (mRNA) when compared with the unbound fraction: when [³H]uridine was present in the light induced sample and [¹⁴C]uridine in the dark control, in the bound material the ³H/¹⁴C ratio was found to be higher than in the unbound fraction and vice versa. No such shift was observed, when both sample and control were kept in the dark. Our data are interpreted to provide evidence for photoinduced de novo synthesis of mRNA.Abbreviations CHI cycloheximide - CTAB N-acetyl-N,N,N-trimethylammoniumbromide - poly(A) poly-adenylic acid - Butyl-PBD 2-(4-t-Butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole