Formation Of Messenger RNA Research Articles

Hierarchical Assembly of Single-Stranded RNA.

Single-stranded RNA (ssRNA) plays a major role in the flow of genetic information-most notably, in the form of messenger RNA (mRNA)-and in the regulation of biological processes. The highly dynamic nature of chains of unpaired nucleobases challenges structural characterizations of ssRNA by experiments or molecular dynamics (MD) simulations alike. Here, we use hierarchical chain growth (HCG) to construct ensembles of ssRNA chains. HCG assembles the structures of protein and nucleic acid chains from fragment libraries created by MD simulations. Applied to homo- and heteropolymeric ssRNAs of different lengths, we find that HCG produces structural ensembles that overall are in good agreement with diverse experiments, including nuclear magnetic resonance (NMR), small-angle X-ray scattering (SAXS), and single-molecule Förster resonance energy transfer (FRET). The agreement can be further improved by ensemble refinement using Bayesian inference of ensembles (BioEn). HCG can also be used to assemble RNA structures that combine base-paired and base-unpaired regions, as illustrated for the 5' untranslated region (UTR) of SARS-CoV-2 RNA.

Expression of the genes of non-specific immune response in the body of gallus gallus domesticus under the influence of immunodepressive vaccine viruses

Relevance. The body reacts to the impact of infectious agents by activating the processes of gene expression in cells and tissues of various organs, which results in the formation of messenger RNA, complementary to the DNA of the expressed genes. This article discusses the effect of vaccine viruses of infectious bursal disease and infectious anemia of chickens on the morphology of target organs of the immune system of chickens, as well as the expression of a number of key genes of nonspecific immune response in the cells of these organs.Methods. As an example of a vaccine virus for infectious bursal disease, an immunocomplex vaccine against infectious bursal disease from the VNIVIP strain was taken; as a sample of a vaccine virus for infectious anemia in chickens, the Nobilis® CAV P4 vaccine manufactured by MSD Animal Health was taken.Results. It was concluded that vaccine viruses come into contact with target organs (the bursa of Fabricius and thymus), causing a number of pathological changes. The expression of the immune genes IL8L2, PTGS2, IRF7 was also determined as the main genes responsible for the synthesis of antiviral and inflammatory proteins. Based on the results of the studies, it was concluded that the IL8L2 and PTGS2 genes responsible for the synthesis of inflammatory components are actively expressed when the cells are exposed to the viruses of infectious anemia of chickens and infectious bursal disease. The expression of the IRF7 gene in the immune organs of the experimental groups of chickens did not practically differ from the level of expression in the target organs of the control birds due to the immunosuppressive effect of the viruses.

Inhibition of the Eukaryotic 80S Ribosome as a Potential Anticancer Therapy: A Structural Perspective.

Simple SummaryUnravelling the molecular basis of ribosomal inhibition by small molecules is crucial to characterise the function of potential anticancer drugs. After approval of the ribosome inhibitor homoharringtonine for treatment of CML, it became clear that acting on the rate of protein synthesis can be a valuable way to prevent indefinite growth of cancers. The present review discusses the state-of-the-art structural knowledge of the binding modes of inhibitors targeting the cytosolic ribosome, with the ambition of providing not only an overview of what has been achieved so far, but to stimulate further investigations to yield more potent and specific anticancer drugs.Protein biosynthesis is a vital process for all kingdoms of life. The ribosome is the massive ribonucleoprotein machinery that reads the genetic code, in the form of messenger RNA (mRNA), to produce proteins. The mechanism of translation is tightly regulated to ensure that cell growth is well sustained. Because of the central role fulfilled by the ribosome, it is not surprising that halting its function can be detrimental and incompatible with life. In bacteria, the ribosome is a major target of inhibitors, as demonstrated by the high number of small molecules identified to bind to it. In eukaryotes, the design of ribosome inhibitors may be used as a therapy to treat cancer cells, which exhibit higher proliferation rates compared to healthy ones. Exciting experimental achievements gathered during the last few years confirmed that the ribosome indeed represents a relevant platform for the development of anticancer drugs. We provide herein an overview of the latest structural data that helped to unveil the molecular bases of inhibition of the eukaryotic ribosome triggered by small molecules.

299. Efficient Functional Oxidase Correction after CRISPR-Oligomer Gene Repair in X-CGD Patient Hematopoietic Stem Cells (HSC) Using Non-Viral, cGMP Compliant, Scalable, Closed System

Gene therapy using integrating viral vectors in hematopoietic stem cells (HSC) has shown clinical benefit in genetic diseases. The safety concerns associated with random integration and the lack of gene expression regulation remain key challenges with use of viral vectors. Efficient and target-site specific correction of mutation(s) in patient HSC genomic DNA using non-viral methods may improve safety and gene expression regulation. We and others have previously reported that loading of Nucleases in the form of messenger RNA (mRNA) results in low toxicity and efficient functional gene editing when using MaxCyte's rapid, automated, cGMP and regulatory compliant, and closed cell loading platform. This platform has been cleared for use in human clinical trials for multiple applications of targeted gene editing in stem cells and immune cells.We report herein that transfecting CRISPR (Cas9+gRNA) mRNA along with donor oligomer specific to a hotspot mutation in the gp91phox gene (CYBB) located on exon 7 associated with the X-linked form of Chronic Granulomatous Disease (X-CGD), using MaxCyte GT System, results in efficient repair of the 676T (stop codon) to 676C (Arginine) mutation, resulting in gp91 protein expression and associated oxidase activity.Plasmids encoding Cas9 and gRNA were purchased from the Genomic Engineering Center at Washington University (St. Louis, MO). The mRNA encoding Cas9 and gRNA were synthesized at MaxCyte using mMESSAGE mMACHINE® T7 Ultra kit, (Ambion, Austin, TX). Patient EBV-transformed B cell line (B-LCL) and patient HSC were obtained under NIAID IRB approved protocol after patient written informed consent. The cells were cultured in RPMI-1640+10% FBS+2mM L-glutamine and StemSpan medium (Stem Cell Technologies, BC, Canada) supplemented with 100ng/ml SCF, Flit3L and TPO, respectively. We first optimized transfection conditions with the X-CGD patient B-LCL. It was found that B-LCL can be efficiently transfected with CRISPR and donor oligomer. Transfected B-LCL exhibit 80±6% viability, and maintained cell proliferation rate identical to control cells. Cel-1 assay shows 30-40% (N=8) efficiency of specific-site gene editing. Using donor oligomer containing a HindIII restriction site, it was determined that the DNA integration efficiency in Exon 7 was 35±8% (N=3). Using donor oligomer with the removal of HindIII restriction site, the expression of functional gp91 protein as determine by flow cytometry was 9±3% (N=3). These developed protocols were used to transfect HSC obtained from the same CGD patient (N=1). Following in vitro myeloid differentiation of gene mutation-repaired CGD HSC, 6.3% of the differentiating cells containing neutrophils and monocytes were oxidase positive in the dihydrorhodamine (DHR) flow cytometry oxidase function assay. These observations demonstrated restoration of phagocyte oxidase activity from the gene repair. Work is in progress to optimize and achieve clinical scale-up of the process which may have broad applicability to the treatment of monogenic diseases.

Exosomes: a role for naturally occurring nanovesicles in cancer growth, diagnosis and treatment.

Exosomes are 30-100 nm bodies secreted from almost all types of cells into the extracellular spaces. They enclose in their lumen active genetic information in the form of messenger RNA (mRNA), micro RNA (miRNA), DNA and active peptides that are representative of the parental cell and can be isolated from different body fluids. Exosomes can participate in inter-cellular communication by trafficking molecules to their target cells. Because they can stably carry cargo including miRNA, mRNA, and proteins and can pass through stringent biological barriers (e.g., blood brain barrier) without eliciting an immune response, they are considered as an ideal acellular vehicle for drug delivery. In this review, we describe the structure and biogenesis of exosomes and new directions related to their role in diagnosis and treatment of diseases, especially for cancer. We also discuss potential challenges associated with exosomes that should be addressed before exosome-based therapy can be applied to clinical settings.

What is our level of knowledge about the genome today

Elucidating the sequence of the human genome marked the beginning of a new phase of understanding of human biology. The pathway from genotype to phenotype, through which the information contained in the DNA is transcribed in the form of messenger RNA (mRNA), and then translated into proteins, is a complicated one, and does not happen in a straight line. Furthermore, most of the mechanisms guiding this complexity have yet to be unravelled. From the concept of 'gene,' to the different types of information that are encoded in the genomic DNA in our nucleus, to epigenetics, this article summarises our current level of knowledge, but also takes note of what we do not yet know as well as the future perspectives in genome studies. Keywords : flow of genetic information ∙ gene expression ∙ DNA regulation ∙ topological association domains ∙ genetic networks ∙ epigenetics

Direct Observation of Distinct A/P Hybrid-State tRNAs in Translocating Ribosomes

Transfer RNAs (tRNAs) link the genetic code in the form of messenger RNA (mRNA) to protein sequence. Translocation of tRNAs through the ribosome from aminoacyl (A) site to peptidyl (P) site and from P site to exit site is catalyzed in eukaryotes by the translocase elongation factor 2 (EF-2) and in prokaryotes by its homolog EF-G. During tRNA movement one or more “hybrid” states (A/P) is occupied, but molecular details of them and of the translocation process are limited. Here we show by cryo-electron microscopy that a population of mammalian ribosomes stalled at an mRNA pseudoknot structure contains structurally distorted tRNAs in two different A/P hybrid states. In one (A/P′), the tRNA is in contact with the translocase EF-2, which induces it. In the other (A/P″), the translocase is absent. The existence of these alternative A/P intermediate states has relevance to our understanding of the mechanics and kinetics of translocation.

Intron Removal Requires Proofreading of U2AF/3' Splice Site Recognition by DEK

Discrimination between splice sites and similar, nonsplice sequences is essential for correct intron removal and messenger RNA formation in eukaryotes. The 65- and 35-kD subunits of the splicing factor U2AF, U2AF65 and U2AF35, recognize, respectively, the pyrimidine-rich tract and the conserved terminal AG present at metazoan 3' splice sites. We report that DEK, a chromatin- and RNA-associated protein mutated or overexpressed in certain cancers, enforces 3' splice site discrimination by U2AF. DEK phosphorylated at serines 19 and 32 associates with U2AF35, facilitates the U2AF35-AG interaction and prevents binding of U2AF65 to pyrimidine tracts not followed by AG. DEK and its phosphorylation are required for intron removal, but not for splicing complex assembly, which indicates that proofreading of early 3' splice site recognition influences catalytic activation of the spliceosome.

What's new in translation initiation? The first translation determines the fate of mRNA.

The two terms 'translation' and 'protein synthesis' are interchangeable in describing the process whereby the genetic code in the form of messenger RNA (mRNA) is deciphered such that amino acids cognate with the triplet code are joined end to end to form a peptide chain. However, new data suggest that the initial act of translation on newly synthesised mRNA also functions to proofread mRNA for errors. Aberrant mRNAs detected in this way are rapidly degraded before their encoded proteins impede normal cell function. Initiation of surveillance translation appears to differ from that of regular protein synthesis in three ways: (i) composition of the substrate; (ii) temporal and spatial restrictions; (iii) factors used to recruit the ribosome. This review discusses translational aspects of mRNA surveillance, primarily in the context of the mammalian system, although much information has come from studies in yeast and other organisms.

Molecular mechanisms of corticosteroids in allergic diseases.

Molecular mechanisms of corticosteroids in allergic diseases.

Effect of lazaroid U-74389G and methylprednisolone on endotoxin-induced shock in mice

<h2>Abstract</h2> <b>Background:</b> Lazaroids are nonglucocorticoid analogs of methylprednisolone with multiple actions. We investigated whether lazaroid U-74389G could attenuate endotoxin-induced liver injury. We hypothesized that U-74389G treatment may protect against hepatic injury by suppressing proinflammatory gene up-regulation through inhibition of activation of nuclear factor κB (NF-κB). We also compared the efficacy of U-74389G with methylprednisolone in endotoxin-induced liver injury. <b>Methods:</b> Lipopolysaccharide (<i>Escherichia coli</i>, 30 mg/kg given intraperitoneally) was administered to male ICR mice, and U-74389G (3 mg/kg intraperitoneally) or methylprednisolone (30 mg/kg intravenously) was administered simultaneously. Phosphate-buffered saline solution (0.15 mL intravenously) was administered to mice that served as a control group. <b>Results:</b> U-74389G and methylprednisolone treatment significantly increased survival rates 48 hours after lipopolysaccharide injection and protected against lipopolysaccharide-induced liver injury in vivo, as indicated by the decreased hepatic lipid peroxidation, tumor necrosis factor-α, and inducible nitric oxide synthase messenger RNA formation, hepatic enzyme release, and neutrophil infiltration in the liver. U-74389G and methylprednisolone also showed inhibitory effects on NF-κB activation in the liver. <b>Conclusions:</b> These findings suggest that U-74389G can suppress proinflammatory gene up-regulation through inhibition of NF-κB activation and that it is a promising new antioxidant drug for the treatment of endotoxin shock. (Surgery 1999;125:421-30.)

Effect of lazaroid U-74389G and methylprednisolone on endotoxin-induced shock in mice

Background: Lazaroids are nonglucocorticoid analogs of methylprednisolone with multiple actions. We investigated whether lazaroid U-74389G could attenuate endotoxin-induced liver injury. We hypothesized that U-74389G treatment may protect against hepatic injury by suppressing proinflammatory gene up-regulation through inhibition of activation of nuclear factor κB (NF-κB). We also compared the efficacy of U-74389G with methylprednisolone in endotoxin-induced liver injury. Methods: Lipopolysaccharide ( Escherichia coli, 30 mg/kg given intraperitoneally) was administered to male ICR mice, and U-74389G (3 mg/kg intraperitoneally) or methylprednisolone (30 mg/kg intravenously) was administered simultaneously. Phosphate-buffered saline solution (0.15 mL intravenously) was administered to mice that served as a control group. Results: U-74389G and methylprednisolone treatment significantly increased survival rates 48 hours after lipopolysaccharide injection and protected against lipopolysaccharide-induced liver injury in vivo, as indicated by the decreased hepatic lipid peroxidation, tumor necrosis factor-α, and inducible nitric oxide synthase messenger RNA formation, hepatic enzyme release, and neutrophil infiltration in the liver. U-74389G and methylprednisolone also showed inhibitory effects on NF-κB activation in the liver. Conclusions: These findings suggest that U-74389G can suppress proinflammatory gene up-regulation through inhibition of NF-κB activation and that it is a promising new antioxidant drug for the treatment of endotoxin shock. (Surgery 1999;125:421-30.)

Correlation between potentiation of AP1 DNA binding and expression of c-Fos in association with phosphorylation of CREB at serine133 in thalamus of gerbils with ischemia

Protein biosynthesis is mainly under the control at the level of gene transcription in eukaryotes. Transcription factors are nuclear proteins with abilities to modulate the activity of RNA polymerase II which is responsible for the formation of messenger RNA from double stranded DNA in the cell nuclei. Binding of a radiolabeled oligonucleotide probe for the transcription factor activator protein-1 (AP1) was transiently potentiated 1 to 6 h after the recirculation of blood supply in the thalamus and striatum, but not in the entorhinal cortex, olfactory bulb, frontal cortex, cerebellar cortex and medulla-pons, in gerbils with transient global forebrain ischemia for 5 min, in addition to the hippocampal subregions. The ischemic insult not only increased the immunoreactivity with an antibody against cyclic AMP response element binding protein (CREB) phosphorylated at serine133, but also induced the expression of both c-Jun and c-Fos family proteins 3 h after the recirculation in the thalamus. Limited proteolysis by Staphylococcus aureus ( S. aureus) V8 protease revealed the expression of different partner proteins of AP1 in response to ischemic signals in the thalamus. Moreover, ischemia for 2 min led to more prolonged elevation of AP1 binding in the thalamus at least up to 12 h after the reperfusion than that seen with ischemia for 5 min. These results suggest that potentiation of AP1 DNA binding may at least in part involve mechanisms associated with the expression of c-Fos protein through phosphorylation of CREB at serine133 in the thalamus of gerbils with ischemia.

Protease Inhibitors as Potential Therapeutic Agents for AIDS

A decade since the epidemic of the acquired immunodeficiency syndrome (AIDS) was first recognized, a wealth of information has accumulated on the molecular biology of the causative agents, the human immunodeficiency viruses (HIV). Of particular interest is knowledge of the viral enzymes involved in the formation of new virus particles. Such enzymes constitute attractive targets for efforts aimed at selecting agents that interfere with virus multiplication and subsequent spread and pathogenesis. Already, several agents that inhibit the viral reverse transcriptase (e.g., nucleoside analogs such as Zidovudine) have proved to have a beneficial effect on the course off the disease, but their prolonged use has been associated with significant toxicity and the emergence of resistant mutants. A second enzyme that has recently attracted attention is the virus-coded protease. This enzyme is involved in the cleavage of viral precursor polyproteins into the final products that constitute the mature virus particle. Protease inhibitors interfere with the process of virus maturation which is required for the formation of infective virus particles. Several custom-made inhibitors with a high selective action against HIV protease have been produced recently. They are nonhydrolyzable peptide analogs that mimic the cleavage sequences of the natural substrate of the enzyme during the transition state of the cleavage reaction. It is hoped that a similar selectivity in vivo may make protease inhibitors a promising new category of AIDS therapeutics.

RNA splicing as an error-screening mechanism

Eukaryote nuclear genes are generally split into coding (exon) and noncoding (intron) regions. During the formation of messenger RNA the introns are precisely excised and the exons religated. A widely accepted explanation for the split structure of eukaryotic genes is that proposed by Gilbert who hypothesized that the division of coding information into small units speeded up the rate of protein evolution by allowing for the recombination of the independent peptide domains encoded by these units ("exon shuffling"). However it has recently become clear that the exon:intron structure of genes most likely preceded the uninterrupted form. This makes it difficult to accept Gilbert's argument as it applies to the origin(s) of split genes since early genes were very inaccurately copied and a highly error-prone system needs less variation not more. Here I propose that split genes and the concomitant process of RNA splicing arose as a mechanism for maintaining the stability of the genetic information in the face of a high level of noise in the gene copier mechanism.

Control of biologically active interleukin 2 messenger RNA formation in induced human lymphocytes.

The regulation of human interleukin 2 (IL-2) mRNA production in induced normal lymphocytes was studied by following the expression of isolated mRNA in microinjected oocytes of Xenopus laevis. Mitogenic stimulation results in the appearance of greatly increased levels of IL-2 mRNA activity. This process requires de novo transcription. Induction is followed promptly by a shutoff of active IL-2 mRNA formation. This shutoff requires the synthesis of a protein repressor and can be prevented by cycloheximide, an inhibitor of translation. The presence of cycloheximide leads to extensive superinduction of IL-2, concomitant with an increase in active IL-2 mRNA formation up to 30-fold over normal levels. The repressor appears to be short-lived, as the addition of cycloheximide after shutoff leads to an immediate resumption of active IL-2 mRNA formation. The shutoff mechanism is restored rapidly upon removal of cycloheximide. The repressed state is readily reversed also by reinduction of the cells, even soon after shutoff has occurred, without a refractory period. The accumulated active IL-2 mRNA decays with a half-life of about 20 hr. The net result is the generation of a relatively short wave of IL-2 mRNA activity, demonstrating the tight control of IL-2 gene expression.

RNA processing comes of age.

During the past two decades, an awareness of the importance of RNA processing has evolved as part of the quest to understand how living cells express the information encoded in their genes . As the knowledge of gene expression has expanded, we have come to realize that the old central dogma of DNA --+ RNA -+ protein is embellished with elegant and intricate design features, many of which are revealed in the processing of primary gene transcripts into the functional forms of RNA. The production of the two large structural RNA components of the ribosome (rRNAs), the synthesis of transfer RNA (tRNA), and the formation of messenger RNA (mRNA) in higher organisms all involve rather elaborate processing reactions, including nucleolytic cleavages, ligations, terminal additions, and nucleoside modifications. A raison d'etre for processing is readily apparent in the case of the coordinate production of rRNA components from a single transcriptional unit and the synthesis of mRNA from noncontiguous genetic elements . However, the purpose of the polyadenylate and methylated cap structures that are added to the termini of mRNA and the modification of internal nucleotides in most RNA species is less clear . These structural alterations may serve to improve the stability of the RNA and the efficiency of its function, but they might also be implicated in more subtle forms of discriminative regulation that are yet to be discovered . In any event, it is clear that RNA processing constitutes a major cellular activity and an integral part of the mechanism ofgene expression. In this essay I shall try to trace the evolution of our concepts of RNA processing in relation to the contemporary issues of cellular and molecular biology and to the introduction of key experimental tools which were critical to the development of these concepts . My idea for treating the subject in this way came from an engaging article on the nucleolus by a former colleague and source of inspiration, Jack Schultz (1). It is my intention to provide both a historical and a reasonably up-todate overview of the subject without the burden of extensive detail . Fortunately, there are several recent reviews to which the reader can refer for a more comprehensive coverage of particular aspects of RNA processing (2-7) .

Process of cap formation of messenger RNA by vaccinia virus particles carrying an organized enzymes system.

Vaccinia virus mRNAs carry the cap structure m7G5'pppAm- or m7G5'pppGm- at the 5'-terminus, which is synthesized by a series of RNA polymerase and capping enzymes contained in the virus particle. The process of the cap formation at the 5'-terminus of mRNA was studied using an in vitro system under similar conditions to those of vaccinia virus multiplication in its host cell. After adding a methyl-group donor, methyl-3H-S-adenosylmethionine, the oligonucleotides, which were the de novo synthesized 5'-terminal part of mRNA, were isolated from the RNA-synthesizing virion at appropriate time intervals, and were analysed. The 5'-5' confronting nucleotides with 2'-O-methylation, G5'pppAm and G5'pppGm, were found with the completed cap structure, m7G5'pppAm and m7G5'pppGm. The confronting nucleotides with only 7-methyl guanine as a methylated component, m7G5'pppA and m7G5'pppG, were not detected at any incubation time, and it was concluded that methylation at the 2'-position of the 5'-terminal purine nucleoside of mRNA precedes methylation of the 7-position of the blocking guanosine. This result is different from that obtained using the enzymes isolated from vaccinia virus (Moss et al., 1976) and also from the results obtained using other kinds of virus particles, which carry RNA polymerase and capping enzymes. These differences may be due to the specific organization of a series of capping enzymes and RNA polymerase in each virus particle.

N-6-methyl-adenosine in adenovirus type 2 nuclear RNA is conserved in the formation of messenger RNA

In the biogenesis of adenovirus type 2 messenger RNAs, methylation occurs at the 5′ end (cap) and to internal adenosine residues to yield N 6-methyl-adenosine (m 6A) (Sommer et al., 1976; Moss & Koczot, 1976; Wold et al., 1976). The kinetics of accumulation of 3H from methyl-labeled methionine and 14C from uridine into Ad-2 † † Abbreviation used: Ad-2, adenovirus type 2. -specific RNA was measured late in Ad-2 infection. As reported previously (Nevins & Darnell, 1978 a), the rate of accumulation of [ 14C]uridine label in nuclear RNA was approximately four- to fivefold faster than in the cytoplasmic RNA, indicating a conservation of about 20% for the total RNA. The initial rates of [ 3H]methyl label in m 6A in nuclear RNA and in the cytoplasmic RNA were approximately equal, suggesting a complete (or nearly complete) conservation of m 6A. In accord with the accumulation kinetics, the ratio of 3H to 14C was higher in cytoplasmic RNA than in nuclear RNA that hybridized to equivalent regions of the Ad-2 DNA. A mathematical model was designed to evaluate the accumulation of methyl label in m 6A, taking into consideration the three major parameters that affect the accumulation curves: equilibration of the S-adenosyl-methionine pool, the nuclear dwell time of sequences destined to be mRNA, and the cytoplasmic stability of mRNA. The half-time ( t 1 2 ) for pool equilibration was determined experimentally to be 22 minutes and the nuclear dwell time and the mean life-time of cytoplasmic mRNA were estimated from 14C label to be about 30 and 70 minutes, respectively. The model gave an excellent fit to the data when the t 1 2 for pool equilibration time of 24 ± 2 minutes, a nuclear dwell time of 25 ± 10 minutes, and a mean cytoplasmic mRNA life-time of 75 ± 30 minutes were used to evaluate accumulation curves. Even when data from a restricted region of the genome, 40.5–52.6 , which encodes the main portion of at least five 3′ co-terminal mRNAs whose spliced junction with the tripartite leader sequence varies from 38, 40, 43, 45 , and 48 was analyzed, it appeared that m 6A was conserved. Finally, m 6A was found to be added in a brief label (3.5 min) mainly to nuclear molecules that were longer than any cytoplasmic RNA. The conservation of m 6A and its addition prior to splicing raise the possibility that internal methylations are involved, in the formation of mRNA.

Implications of RNA⋅RNA Splicing in Evolution of Eukaryotic Cells

The differences in the biochemistry of messenger RNA formation in eukaryotes compared to prokaryotes are so profound as to suggest that sequential prokaryotic to eukaryotic cell evolution seems unlikely. The recently discovered noncontiguous sequences in eukaryotic DNA that encode messenger RNA may reflect an ancient, rather than a new, distribution of information in DNA and that eukaryotes evolved independently of prokaryotes.