Polyadenylylation and transcription following fertilization

Identification and properties of the 38 000-Mr poly(A)-binding protein of non-polysomal messenger ribonucleoproteins of cryptobiotic gastrulae of Artemia salina

The Mr-38 000 poly(A)-binding protein interacts with synthetic and natural RNA. A sequence-independent stoichiometry of one protein per 8 - 12 nucleotides is measured by filter binding and sucrose gradient centrifugation. Specificity for the poly(A) sequence is demonstrated from poly(A)/RNA mixing experiments. The poly(A)-binding protein has been identified as the helix-destabilizing protein HD40[Marvil, D. K., Nowak, L. and Szer, W. (1980) J. Biol. Chem. 255, 6466 - 6472] and is characterized by the existence of at least seven ionic species with a pI ranging from 9.2 to 6.6. Acidic ionic species are generated by phosphorylation with mRNP-associated protein kinase. Different ionic species are present on free mRNP and ribosomes-mRNP preinitiation complexes. The poly(A)-binding protein affects mRNA translation and (A)4 polyadenylation. The multifunctionality of the protein is discussed.

Heat shock induced alterations in polyadenylate metabolism in Drosophila melanogaster

We have studied the effect of heat shock on poly(adenylic acid) [poly(A)] metabolism in Drosophila melanogaster cells by using hybridization of ribonucleic acid (RNA) samples to [3H]poly(uridylic acid). Shortly after heat shock begins, cytoplasmic poly(A) decays rapidly. Two components were detected. Component I constitutes 46% of the total cytoplasmic poly(A) and decays with a half-life of 10 min. Component II (54% of total) is more stable. A half-life was not estimated for component II because new synthesis was not blocked. Studies on the size of cytoplasmic poly(A) indicate component I is completely degraded while component II remains essentially unchanged. Nuclear poly(A) increases rapidly, peaking at 2 or 3 times the normal level after 90 min of heat shock. Studies on the size of nuclear poly(A) indicate the increase is not due to addition of poly(A) to existing poly(A) segments nor appreciably to newly synthesized RNA unless transit time is markedly increased. We conclude that nuclear poly(A) is added in large part to already existing nonadenylated primers. Studies with RNA and protein synthesis inhibitors show RNA and protein synthesis are not required for the changes in poly(A). As the temperature is raised above 34--35 degrees C, the effect on poly(A) metabolism becomes more severe. Changes in external pH, without increased temperature, also alter poly(A) levels. Poly(A) changes may therefore be a rapid response to a variety of physiological factors.

Message sequences and short repetitive sequences are interspersed in sea urchin egg poly(A)+ RNAs

At least half of the mass and most of the different single-copy maternal mRNA sequences in the egg are covalently associated with transcripts of short repetitive sequences. Only a restricted group of the diverse genomic repeat families are significantly represented. The messages fall into several hundred sets, each containing transcripts from a different repeat family.

Preformed mRNA in Cotyledons of Ungerminated Seeds of Cicer arietinum L

Polyadenylated RNA was isolated from total RNA extracted from cotyledons of ungerminated or 18-hour-germinated chick-pea seeds by affinity chromatography on oligo(dT)-cellulose. Both poly(A)-containing RNA fractions exhibited a template activity when assayed in two cell-free translation systems, wheat germ extracts, and nuclease-treated reticulocyte lysates. Translation of preformed mRNA from cotyledons of dry seeds was completely abolished in the presence of several inhibitors of polypeptide chain initiation and also in the presence of the two "cap" analogues m(7) GTP and m(7) GMP. The patterns of polypeptides synthesized by translation of poly(A)-containing RNAs from cotyledons of ungerminated or 18-hour-germinated seeds, in the wheat germ system, analyzed by electrophoresis and autoradiography, were similar but not identical. It is concluded that cotyledons of dry Cicer arietinum L. seeds contain preformed mRNA.

Cell-free cytoplasmic polyadenylation of oogenic RNA

The products of cell-free ATP incorporation mediated by cytoplasmic fractions prepared from unfertilized sea urchin eggs, anucleate egg halves, nucleate egg halves, emetine-treated fertilized eggs, and four-cell embryos have been characterized to determine to what extent the polymers synthesized are poly(A) and to assess the size distribution of the primers adenylated. As judged by alkaline lability, ribonuclease resistance, and retention on poly(U)-impregnated filters, greater than 92% of the label recovered after RNA extraction is present in poly(A). LiCl fractionation indicates that little, if any, free poly(A) is synthesized or cleaved from RNA primers during the reaction, and that 4S RNA is not an effective initiator. In excess of 85% of the poly(A) is associated with RNA having S-values greater than or equal to 18S. Sedimentation profiles of RNA adenylated in the unfertilized egg and anucleate egg half reactions are identical. Suppression of in vivo protein synthesis by emetine alters the profile of RNA subsequently adenylated in vitro. It is proposed that the apparent constraints on the utilization of cytoplasmic RNA or ribonucleoprotein primers of oogenic origin may be effected by RNA-associated proteins capable of regulating the selection and/or extent of their polyadenylation during early embryogenesis.

Developmental regulation in cotton seed germination: polyadenylation of stored messenger RNA

Evidence that RNA preexisting in the cotyledons of mature cotton seed (stored mRNA) is polyadenylated during the first day of germination is presented, based on three different experimental data sets. First, actinomycin D is found to inhibit 32PO4 incorporation into mRNA-poly(A) by 62%, into mRNA by 70%, but into poly(A) only 30%. Second, far more 32PO4 and [2-3H]adenosine are incorporated into the poly(A) portion of mRNA-poly(A) than into the mRNA portion as would be expected from their relative sizes and base composition. This underlabeling of the mRNA moiety is enhanced when cotyledons are germinated in actinomycin D. However, an expected distribution of the isotopes between the mRNA and poly(A) moieties is found in cotyledons labeled later in germination. Third, spectral measurements of the absolute amount of mRNA-poly(A) accumulated during the first day of germination in cotyledons germinated in actinomycin D are larger than would be expected from the 70% inhibition of mRNA labeling caused by the drug. The three sets of data suggest that over 50% of the total mass of mRNA polyadenylated during early germination exists in the mature seed. Its complexity, however, has not been measured. These data may explain the sensitivity of much of germination enzyme synthesis to inhibition by 3'dAdo during early germination and its insensitivity to actinomycin D during this period.

Post-transcriptional suppression of globin gene expression in cells transformed by avian erythroblastosis virus

Cells transformed by avian erythroblastosis virus were grown in vitro for up to 5 months. After a few days in culture, synthesis of hemoglobin was undetectable and could not be induced by dimethyl sulfoxide. As shown by globin cDNA hybridization to nuclear and cytoplasmic RNA carried to Crot values of 10(5) moles of nucleotide per liter X sec, globin genes in these cells are transcribed into pre-mRNA, but no trace of globin mRNA appears in the cytoplasm. The implications of this observation for schemes of post-transcriptional regulations and viral transformation are discussed.

Actions of aldosterone on polyadenylated ribonucleic acid and Na+ transport in the toad bladder

Polyadenylated ribonucleic acid [poly(A)(+)-RNA] has been isolated from the cytoplasm of the epithelium of the urinary bladder of the toad (Bufo marinus) by oligo-(deoxythymidylate)cellulose chromatography. Aldosterone increased the incorporation of [3H]uridine, and of [3H]uridine and [3H]adenosine (given in combination) into 7S, 12S, and 18S poly(A)(+)-RNA during the first 30 min of the action of the hormone, as defined by either a pulse or pulse-chase sequence. The quantity of cytoplasmic poly(A)(+)-RNA that hybridized to [3H]poly(uridine) was also increased by aldosterone. These results are consistent with the inference of induction of messenger RNA synthesis. This effect was most marked during the first 30 min of the action of the hormone.

Globin mRNA species containing poly(A) segments of different lengths. Their functional stability in Xenopus oocytes

Rabbit globin mRNA species containing poly(A) segments of different lengths were prepared by partial phosphorolysis of mRNA with Escherichia coli polynucleotide phosphorylase. By varying the salt concentration and the time of incubation of the phosphorolysis mixture, as well as performing oligo(dT)-cellulose chromatography at 22 degrees C and at 4 degrees C, globin mRNA preparations containing poly(A) segments of approximately 122, 95, 68, 39, 32, 21, and 16 adenylate residues were obtained. It was found that the functional stability of the mRNA species containing 32 or more adenylate residues after injection into Xenopus laevis oocytes equaled that of the native globin mRNA. On the other hand, the functional stability of mRNA containing an average number of 21 adenylate residues was about 30% of the native mRNA, while that of mRNA containing 16 adenylate residues was as low as poly(A)-free globin MRNA.

The occurrence and distribution of poly(a) ribonucleic Acid in soybean

The occurrence and distribution of poly(A) sequences in the RNA of soybean (Glycine max var. Wayne) have been studied. Only one of the two species of AMP-rich RNA contains poly(A). D-RNA does not contain detectable poly(A) sequences. The TB-RNA is the poly(A) RNA in this system. At least a part (up to 50% or more) of the mRNA in polyribosomes contains a poly(A) sequence. The poly(A) RNA is heterodisperse in size but has a mean size of approximately 18S (2,000 nucleotides) in urea and formamide gels. The poly(A) fragment resulting from ribonuclease A and T(1) digestion migrates as a broad band overlapping the 4 to 5.8S regions of the gels with a mean size of somewhat greater than 5S. No evidence was found for the occurrence of a discrete oligo(A) fragment in the poly(A) RNA; however, oligonucleotides which migrate faster than the poly(A) fraction were observed in preparations which were not bound to oligo(dT) cellulose prior to electrophoresis. This oligonucleotide region was enriched in AMP (up to about 65%) as would be expected after ribonuclease A and T(1) digestion.

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).

Preformed mRNA and the programming of early embryo development

A significant feature of the early development of fertilized echinoderm and amphibian eggs and germinating seed embryos is the utilization of genetic information that has been previously transcribed during oogenesis and seed ripening. When RNA synthesis is suppressed in the early developing embryos by actinomycin D, cordycepin, or alpha-amanitin, there is no effect on the translation of the "preformed mRNA", only a limited number have been thus far identified; microtubule and histone proteins in the fertilized sea urchin egg and carboxypeptidase and isocritric lyase in germinating cottonseed. Data obtained on the protein synthetic pattern at different times after the onset of development suggest that preformed mRNAs are made available to the translational system in a gradual process, thereby providing a molecular basis for the regulation of development. The possibility is considered that polyadenylation of mRNA, a reaction known to occur early after sea urchin fertilization, is responsible for regulating the release of preformed mRNA. It is shown that this reaction (polyadenylation) can be completely suppressed with little effect on the function of preformed mRNA. Finally, it is suggested, at least for the seed embryo system, that the formation of ATP may be a prerequisite for the activation of protein synthesis.