Adenine-rich polymer associated with rabbit reticulocyte messenger RNA

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.

The secondary structure and poly(A) content of globin messenger RNA as a pure RNA and in polyribosome-derived ribonucleoprotein complexes

The conformation in solution of duck and rabbit globin mRNA, and of the duck mRNA in the mRNA - protein particle, has been investigated by optical methods and also by the use of the dye ethidium bromide which becomes highly fluorescent when intercalated into the double-stranded regions of a nucleic acid. On the basis of the properties of this dye and on the ability of homopolyribonucleotides to form double-stranded structures we have, in addition, developed a simple and sensitive assay for the detection and quantitisation of sequences rich in a particular residue that may be present in an RNA chain. In solution, 45 to 60% of the nucleotides of duck globin nRNA were found to be in bihelical regions. A similar degree of secondary structure was found in rabbit globin mRNA (this paper), as well as in calf lens mRNA and mRNAs from ewe mammary gland (other results). All samples of globin mRNA examined in this work containeda sequence of poly(A), which has poly(U) binding properties similar to that of synthetic poly(a): no specific interaction between the poly(A) sequence and the rest of the molecules can be detected. The fraction of adenosine residues within these poly(A) segments represents 4% in rabbit mRNA and 8 to 9% in duck mRNA. An additional adenosine-rich segment interspersed with guanosine and possibly other residues, was also detected in one duck mRNA sample. The RNA in the duck mRNA - protein particle is also highly structured. The melting profile in the range of 20 to 65 degrees C is quite similar to that of free mRNA and the ability of ethidium bromide to intercalate is reduced to the extent of 70%. Yet the dichroic spectra of free and bound mRNA are significantly distinct. These data suggest that free and protein-bound mRNA May have a very similar degree of secondary structure but with distinct detailed conformation in bihelical regions (change in base tilting for example). Direct evidence has been obtained that proteins stick to the poly(A) segment in the particle since the fraction of adenosine residues detectable by our poly(u) titration procedure is reduced to 50% of that observed in the free mRNA.

Presence of polyriboadenylate sequences in pulse-labeled RNA of Escherichia coli

Pulse-labeled RNA isolated from E. coli cells grown on limiting phosphate medium and phosphate-containing medium was analyzed by oligo(dT)-cellulose chromatography and by Millipore binding assay for polyriboadenylate-containing RNA. Whereas poly(A)-containing RNA amounted to as much as 15% of the total pulse-labeled RNA from cells grown on limiting phosphate medium, pulse-labeled RNA from cells grown on phosphate medium gave values around 1.5%. Steady-state labeled RNA from cells grown on limiting phosphate medium contained 1.2% poly(A) RNA. The addition of poly(A) sequences appears to be post-transcriptional. These results strongly favor the view that bacterial mRNAs may contain poly(A) stretches.

Association of the polyadenylate segment of messenger RNA with other polynucleotide sequences in mouse sarcoma 180 polyribosomes

Limited digestion of polysomal RNA with pancreatic ribonuclease releases a structure consisting of poly(A) associated with other polyribonucleotide sequences. This complex can be purified by oligo(dT)-cellulose chromatography. Heating for formamide treatment causes the dissociation of fragments free of poly(A) from the poly(A)-containing components. The two types of fragments tend to reassociate under annealing conditions, and this association is prevented by poly(U). Control experiments indicate that this structure is not an artifact generated during the manipulations. The same structure can be obtained by limited RNase digestion of polyribosomes, followed by deproteinization. The results suggest that the mRNA in polyribosomes may have a defined configuration caused by the interaction of the poly(A) sequence with another segment of the RNA.

Induction of polyadenylate polymerase and differentiation in neuroblastoma cells

Treatment of neuroblastoma cells with dibutyryl-adenosine 3':5'-monophosphate or adenine induced axon formation and a three-fold increase in the polyadenylate, poly(A), content of the polysomal mRNA. The extracted poly(A) contained 90% adenylic acid and showed a mobility of 6--7 S in dodecylsulfate-polyacrylamide gel electrophoresis. Treatment with dibutyryl-adenosine 3':5'-monophosphate or adenine, also induced a 4--6 fold increase in a nuclear enzymic activity that incorporated [3H]ATP to an acid-insoluble polymer in a cell-free system. This polymer, like poly(A) extracted from the polysomal mRNA, was bound at high salt concentration to nitrocellulose filters. [3H]ATP incorporation was Mg2+-dependent, sensitive to ribonuclease and EDTA and resistant to deoxyribonuclease and actinomycin D. There was no incorporation of [3H]UTP or [3H]dTTP and addition of TUP, CTP and GTP did not increase the incorporation of [3H]ATP. 5-Bromodeoxyuridine induced axon formation of neuroblastoma cells and poly(A) polymerase activity, without increasing the poly(A) content in the polysomal mRNA. The results indicate that induction of axon formation of neuroblastoma cells is associated with an increase in the activity of poly(A) polymerase. It is suggested that the induction of this enzyme may be generally involved in cell differentiation.

RNA processing and RNA tumor virus origin and evolution

The results of molecular hybridization experiments with high-molecular-weight RNA isolated from RNA tumor viruses and DNA from normal cells suggest that RNA tumor virus genomes originate from cell genes. Some RNA tumor viruses (here called class 1) appear to have been generated in recent times in that their RNA is closely related in nucleotide sequence to certain cell genes (class 1 genes). A second class of RNA tumor viruses (here called class 2) is more distantly related to genomic information of normal cells. Structural properties of the RNA of RNA tumor viruses lead us to propose that the tumor virus RNA is originated when RNA transcripts of class 1 genes are processed by a mechanism we call "paraprocessing." We postulate that RNA paraprocessing is normally used only at particular times during differentiation and is characterized by the cytoplasmic appearance of high-molecular-weight RNA chains containing terminal polyadenylic acid (200 residues). Paraprocessing of class 1 gene transcripts in committed or differentiated cells is considered to be aberrant in transcription that can lead to the generation of an RNA tumor virus genome. If the paraprocessed class 1 gene transcript codes for a reverse transcriptase, replication of the RNA becomes possible. Transfer of the replicating RNA to a new cell can result in genetic change such that the virus genome mutates, differing from the original progenitor genes. We propose that this genetic change causes class 1 viruses to become class 2. These ideas are applied to evidence concerning the biology of infection of RNA tumor viruses and concerning the involvement of RNA tumor viruses in human cancer. Genetic change can also occur during the origination of an RNA tumor virus genome by repeated reverse transcription and recombination (45) or by genetic alteration of particularly changeable cell genes ("hot spots") (43).

Pyrimidine-rich oligonucleotides from rat-liver ribosome surface

The distribution of oligonucleotides which are released from rat liver ribosomes by treatment with pancreatic ribonuclease has been studied. Rat liver monoribosomes lost from 15 to 17% of their nucleotides by treatment with pancreatic ribonuclease. This quantity was highly reproducible and did not depend significantly on the temperature (0-20 degrees C) and time (10-120 min) of incubation or on the concentration of enzyme (1:5000-1:50). Whereas the amounts of oligonucleotides liberated was 16%, it was shown by column chromatography that they consisted of 71% mononucleotides, 16% dinucleotides, 6% trinucleotides, 4% tetranucleotides and 2% pentanucleotides and that these oligonucleotides were enriched in uridine, containing approximately half of the uridine residues present in the high-molecular-weitht ribosomal RNA. The high molecular weight of the RNA from ribonuclease-treated ribosomes was preserved until it was heated; after heating, RNA fragments having sedimentation coefficients of 5 S and less were present. It is inferred that the olignucleotides are derived from pyrimidine-rich clusters located in single-stranded "hairpin" loops on the outside surface of the ribosome.

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

Properties and location of poly(A) in Rous sarcoma virus RNA

The poly(A) sequence of 30 to 40S Rous sarcoma virus RNA, prepared by digestion of the RNA with RNase T(1), showed a rather homogenous electrophoretic distribution in formamide-polyacrylamide gels. Its size was estimated to be about 200 AMP residues. The poly(A) appears to be located at or near the 3' end of the 30 to 40S RNA because: (i) it contained one adenosine per 180 AMP residues, and because (ii) incubation of 30 to 40S RNA with bacterial RNase H in the presence of poly(dT) removed its poly(A) without significantly affecting its hydrodynamic or electrophoretic properties in denaturing solvents. The viral 60 to 70S RNA complex was found to consist of 30 to 40S subunits both with (65%) and without (approximately 30%) poly(A). The heteropolymeric sequences of these two species of 30 to 40S subunits have the same RNase T(1)-resistant oligonucleotide composition. Some, perhaps all, RNase T(1)-resistant oligonucleotides of 30 to 40S Rous sarcoma virus RNA appear to have a unique location relative to the poly(A) sequence, because the complexity of poly(A)-tagged fragments of 30 to 40S RNA decreased with decreasing size of the fragment. Two RNase T(1)-resistant oligonucleotides which distinguish sarcoma virus Prague B RNA from that of a transformation-defective deletion mutant of the same virus appear to be associated with an 11S poly(A)-tagged fragment of Prague B RNA. Thus RNA sequences concerned with cell transformation seem to be located within 5 to 10% of the 3' terminus of Prague B RNA.

The polyA regions of hen oviduct RNA

Total RNA from hen oviduct has been hydrolysed with a mixture of T(1) and pancreatic ribonucleases. Poly(A) tracts in the digestion product have been isolated by binding to oligo(dT) cellulose. Of the four major ribonucleotides, the product has been shown to contain only adenylic acid. When separated on polyacrylamide gels, the poly(A) gave two peaks corresponding to average apparent lengths of 270-280 and 540-550 nucleotides.

Translational properties of rabbit globin mRNA after specific removal of poly(A) with ribonuclease H

Highly purified RNase H (RNA.DNA hybrid ribonucleotidohydrolase, EC 3.1.4.34) from calf thymus was used to specifically remove the poly(A) sequences of purified rabbit globin mRNA after its hybridization with poly(dT). The deadenylylated globin mRNA was repurified by a one-step procedure including a nitrocellulose column. The poly(A) size and the content of unmodified mRNA were determined by hybridization with [(3)H]-poly(U), and it could be shown that the RNase H digestion method effectively removes this terminal poly(A) sequence. No difference in activity was found between mRNAs with and without poly(A) to initiate, elongate, terminate, and release newly synthesized globin chains in exogenous-mRNA-dependent, cell-free, protein-synthesizing systems from wheat embryo, ascites Krebs II cells, and rat liver. Furthermore, poly(A)-free globin mRNA competed with the same efficiency as authentic globin mRNA against chick ovalbumin mRNA when translated under total mRNA saturation conditions. It is apparent that the 3'-terminal poly(A) sequence is not necessary to maintain the translationally active secondary and tertiary configuration of the globin mRNA molecule. Preincubation of intact and deadenylylated globin mRNA in the Krebs II ascites translational system indicates that the presence of the poly(A) sequence may stabilize the translationally active mRNA molecule.

Nuclear ribonucleoprotein complexes containing polyadenylate from mouse ascites cells

Nuclear poly(A)-containing RNA of mouse ascites cells can be extracted in the form of 15-17S ribonucleoprotein complexes under conditions in which the bulk of the heterogeneous nuclear RNA is released as 30S complexes. The poly(A)-containing fraction of nuclear extracts has been resolved into two distinct components, 15 and 17 S; neither contains the two polypeptides of 30S ribonucleoprotein. The 17S particle contains approximately six polypeptide species of molecular masses 17,000-30,000 daltons. The 15S complex has four distinct polypeptides of higher molecular mass, including a prominent 80,000-dalton species.

Effects of cytosine arabinoside on differential gene expression in embryonic neural retina. I. Accumulation of glutamine synthetase with suppression of macromolecular synthesis

The analogue of cytidine, cytosine arabinoside (Ara-C), elicited a significant increase in the level of glutamine synthetase (GS) in embryonic chick neural retina in the absence of the steroid inducer of the enzyme. The increase was due to de novo synthesis of GS and was mediated by RNA which accumulated in the presence of the effective concentration of Ara-C. Accumulation of GS did not result from the inhibition of DNA synthesis for which Ara-C is best known. This new effect of Ara-C involves differential suppression of macromolecular synthesis in this system: the concentration of Ara-C which caused maximum GS accumulation suppressed overall protein and RNA syntheses 65-75% without inhibiting the transcription and translation of templates essential for GS synthesis. Withdrawal of Ara-C resulted in restoration of RNA synthesis and cessation of GS accumulation, even though preformed templates for the enzyme were present; however, if all RNA synthesis was arrested with actinomycin D at the time of Ara-C withdrawal, GS continued to accumulate. The results are consistent with the hypothesis that Ara-C differentially affects the activity of structural and regulatory genes involved in the regulation of GS levels in the retina: Ara-C allows transcription of the enzyme-specific templates, but reversibly inhibits the expression of regulatory genes which limit the accumulation of GS.

Fate of mRNA of L-cells infected with mengovirus

Mengovirus infection of L-cells results in an inhibition of host protein synthesis which is detectable in vivo by a decreased rate of incorporation of radioactive amino acids into acid-insoluble material and by a concomitant reduction in polysome content. The inhibition of host protein synthesis occurs early in the infection cycle, at a time when there is little synthesis of viral proteins. In this paper the stability of polyadenylic acid [poly(A)]-containing mRNA of uninfected L-cells and cells infected with mengovirus is compared. Our results suggest that there is no increase in the rate of degradation of cellular mRNA upon virus infection. The continued integrity of host mRNA throughout infection was verified by acrylamide gel electrophoresis.

Characterization of ribonucleic acids from the venom glands of Crotalus durissus terrifucus (Ophidia, Reptilia) after manual extraction of the venom. Studies on template activity and base composition

RNA synthesis in the venom glands of Crotalus durissus terrificus was stimulated by the manual extraction of the venom (milking). RNA was extracted from venom glands activated by milking and fractionated by centrifugation through sucrose density gradients. Template activity for protein synthesis and base composition of the RNA fractions were studied. RNA fractions that sediment between 18S and 4S had the highest template activity. The base composition analysis indicated that the 28S and 18S rRNA have a C+G content of 65.4 and 58% respectively. The ;melting' temperature (T(m)) of DNA in 0.15m-NaCl-0.015m-trisodium citrate, pH7.0, was 85 degrees C, corresponding to a C+G content of 38%. The base ratio of the RNA fractions that showed a high template activity was intermediate between that of rRNA and homologous DNA. The possible role of these fractions in the synthesis of the two main toxins (crotoxin and crotamine) of the South American rattlesnake's venom is discussed.