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Review: ethidium fluorescence assay. Part II. Enzymatic studies and DNA-protein interactions.

Almost all DNA and RNA metabolizing enzymes can be assayed rapidly and very sensitively by exploiting the enhanced fluorescence of ethidium intercalated into duplex DNA or RNA. Denatured DNA and natural RNAs contain duplex regions due to intramolecular hydrogen-bonding and can also be sensitively measured. Where the product is truly single-stranded (e.g. dTn) it can be assayed by adding the appropriate complementary strand (e.g. dAn or rAn). Some of the assays described provide information not readily obtained by other assay procedures. Among the enzymes readily assayed are DNA and RNA polymerases, terminal deoxynucleotidyl transferases, nucleases of all varieties (e.g. single-strand specific, endonucleases including for example AP endonucleases, exonucleases, RNase H, etc.), ligases, topoisomerases including gyrases, and indirectly enzymes such as proteases and superoxide dismutase. DNA binding proteins such as histones and helix destablizing proteins can also be quantitatively assayed.

DNA

Long noncoding RNA GAS5 disrupts intestinal epithelial barrier function by increasing small vault RNA levels.

Disruptions in the integrity of the intestinal epithelium occur commonly in inflammatory bowel disease (IBD) and critical surgical disorders, but the underlying mechanisms remain largely unknown. Here we identified long noncoding RNA GAS5 as a repressor of intestinal mucosal growth and the function of the gut epithelial barrier. The levels of tissue GAS5/Gas5 increased in mouse intestinal mucosa after colitis and septic stress, as well as in human intestinal mucosa from patients with IBD. Transient and tissue-specific knockdown of Gas5 in mice using CRISPR/Cas9 enhanced the renewal of the mucosa of the small intestine, increased the levels of tight junction (TJ) proteins ZO-1, ZO-2, claudin-1, and claudin-2, and improved gut barrier function. Conversely, ectopic overexpression of GAS5 in intestinal organoids and in cultured intestinal epithelium cells decreased the levels of these TJ proteins and caused epithelial barrier dysfunction. Mechanistic studies revealed that GAS5 acted as a transcriptional enhancer of the gene (2. AUTHOR: Do you mean "genes"?) encoding small noncoding vault RNAs (vtRNAs) and that GAS5 repressed TJ expression by increasing the levels of vtRNAs. Together, our results indicate that GAS5 disrupts the integrity of the intestinal epithelium by impairing mucosal growth and epithelial barrier function and that it represses TJ expression, at least in part, via vtRNAs.

Animals

Dual-gRNA CRISPR/Cas9 Deletion of CsDMR6 in Sweet Orange Supported by Improved In Vitro Regeneration.

Huanglongbing (HLB), caused by Candidatus Liberibacter spp., remains the most destructive disease affecting citrus worldwide. To support host-directed genome-editing strategies aimed at reducing susceptibility, we optimized key regeneration steps in Citrus sinensis and validated a dual-gRNA CRISPR/Cas9 approach targeting the susceptibility gene CsDMR6. Juvenile explants of 'Valencia' and hybrid genotypes (CsH1-CsH3) were successfully established in vitro, and shoot elongation was markedly improved by supplementing Citrus Shoot Multiplication (CiSM) medium with 1 mg L-1 GA3. Callus induction was most efficient in Citrus Callus Induction (CiCM) medium under dark conditions, while a 48 h NAA pulse (100 µM) significantly enhanced rooting, increasing efficiencies to 37.1% in 'Valencia' and 52.9% in CsH1. Two guide RNAs targeting conserved regions of CsDMR6 were designed and shown to be identical across all evaluated genotypes. The dual-gRNA cassette was assembled into a CRISPR/Cas9 geminivirus-based vector and transiently delivered into sweet orange leaf tissue via Agrobacterium. GFP fluorescence verified construct expression, and PCR amplification across the target region produced a diagnostic ~447 bp fragment corresponding to the expected ~5.8 kb deletion. Sanger sequencing confirmed precise junction formation between the two cut sites. These results demonstrate efficient large-fragment deletion of CsDMR6 in sweet orange and establish an experimentally validated, genotype-compatible regeneration and editing platform. This study provides a transient validation of the dual-gRNA system and establishes the technical foundation required for future stable, non-transgenic edited lines. Together, these advances support the downstream functional evaluation of CsDMR6 loss-of-function alleles under HLB pressure.

CRISPR/Cas9

Enhanced exonuclease-Cas9 systems promote multiple nucleotide deletions with higher efficiency and broader targeting scope in plants.

CRISPR-Cas9 is a widely used platform for plant genome editing, but its outcomes are typically dominated by small insertions and deletions (indels). Such limited mutation profiles restrict its utility in functional studies of non-coding RNAs and regulatory elements, such as microRNAs (miRNAs), untranslated regions (UTRs), and promoter sequences, where larger sequence disruptions are often required. Here, we developed enhanced exonuclease-Cas9 platforms, termed multiple nucleotide deletion Cas9 (MND-Cas9) systems, for efficient generation of large deletions in rice. By screening four exonucleases (RecJ, T5, TREX2, and SbcB), we established MND-Cas9v1 systems based on TREX2 or SbcB that produced substantially larger deletions without reducing editing efficiency. Further optimization with an inserted DNA-binding domain (DBD) between Cas9 and exonuclease yielded MND-Cas9v2, which simultaneously enhanced efficiency and deletion size. To expand PAM compatibility, we introduced PAM-relaxed Cas9-NG and SpG variants, generating MND-Cas9-NG/SpGv2 systems with broader targeting scope and superior performance compared to their parental nucleases. Finally, we demonstrated the utility of these systems in two applications: MND-Cas9v2 efficiently knocked out the miRNA gene OsMIR530, producing larger seeds, and generated extended deletions in the 3'UTR of OsGhd2, which upregulated its expression and increased grain size. These results demonstrate that MND-Cas9 systems enable high-efficiency generation of extended deletions and facilitate functional analyses of non-coding RNAs and regulatory sequences. Overall, this work establishes a versatile and expandable exonuclease-Cas9 platform that substantially broadens the mutational spectrum and application potential of CRISPR-Cas9 for plant genome engineering.

CRISPR-Cas Systems

Global lncRNA expression profiles in medulloblastoma reveal crucial lncRNA-oncogene interactions in Sonic hedgehog and Group 4.

BACKGROUND: Advances in multi-omic studies have improved medulloblastoma (MB) characterization, yet novel molecular biomarkers are needed to refine tumor biology and therapeutic strategies. Current profiling mainly targets the protein-coding genome, while the potential of noncoding regions remains unexplored. This study aims to identify long noncoding RNAs (lncRNAs), emerging as crucial regulators in MB, as potential key biomarkers specific to molecular group, enhancing understanding of MB's genomic landscape. METHODS: RNA-seq data from 54 Spanish MB patients (C1) and 207 public samples (C2) were analyzed to profile lncRNAs. Expression and Weighted Gene Coexpression Network (WGCNA) analyses were performed to identify lncRNA-oncogene interactions. Group-specific interactions were examined to infer their role in MB pathogenesis and highlight potential lncRNA involvement in disease mechanisms. RESULTS: LncRNA expression profiles identified 4 clusters corresponding to the MB molecular groups, confirming their potential as biomarkers. Expression and WGCNA analyses revealed group-specific lncRNAs for Sonic hedgehog (SHH), Group 3 (Gr3), and Group 4 (Gr4) MB. Lnc-SMARCA2 was exclusively upregulated in SHH MB, and associated with ATOH1 and PDLIM3, key cilium regulators of this group's cell of origin. In Gr4 MB, MGC32805 and LOC107986446 were upregulated and linked to SNCAIP, potentially influencing PRDM6 activation via enhancer hijacking. Additionally, a 5-lncRNA signature linked to phototransduction was exclusive to Gr3, offering insights into its lineage switch and molecular regulation. CONCLUSIONS: Lnc-SMARCA2 and, MGC32805 and LOC107986446, are exclusively deregulated in SHH and Gr4 MB, respectively, and directly associated with group-specific MB oncogenes, representing promising novel biomarkers and therapeutic targets in MB.

cancer biomarkers

Transcription of host-substituted simian virus 40 DNA in whole cells and extracts.

Viral transcriptional complexes were extracted from the nuclei of monkey kidney cells infected with wild-type simian virus 40 (SV40) or a variant strain containing a high proportion of host-substituted DNA molecules. The RNAs synthesized by these complexes in an in vitro system were analyzed for their content of SV40 and host sequences by a technique of sequential hybridization to plaque-purified and substituted viral DNAs. The relative labeling of the two types of sequences was commensurate with their proportion in the viral DNA (about 20% host). The substituted virus contains both reiterated and unique types of cellular sequences, and both kinds appeared to be transcribed. Transcripts of the substituted sequences formed a much smaller proportion of the virus related RNA recovered from intact infected cells, suggesting that host sequence transcripts are synthesized but rapidly degraded in the whole cell. The alternative, that transcription of these sequences is artificially enhanced in the in vitro system, cannot be rigorously excluded. We compared the self-annealing of viral RNAs from nuclear extracts of cells infected with wild-type and substituted viruses; transcripts labeled both in vivo and in vitro showed a two- to threefold-higher level of self-annealing in the case of the variant than in the case of wild type SV40.

Base Sequence

Multiplexed perturbation enables scalable pooled screens.

CRISPR-based genetic perturbation screens have revolutionized the ability to link genes to cellular phenotypes with unprecedented precision and scale; however, conventional pooled CRISPR screens require large cell numbers to achieve adequate sgRNA representation, posing technical and financial challenges. Here, we investigate the impact of co-delivery of multiple guide RNAs via high multiplicity of infection (MOI) in pooled CRISPR interference screens as a strategy to enhance screening efficiency while reducing cell numbers. We systematically evaluate screen performance across varying MOIs, assessing the effects of multiplexing on knockdown efficiency, sgRNA representation and potential interference of multiple sgRNA phenotypes. Our data demonstrate that sgRNA multiplexing (MOI 2.5-10) can maintain screen performance while enabling significant reductions in cell number requirements. We further apply these optimized conditions to conduct a genome-wide CRISPR screen for regulators of the intracellular adhesion molecule ICAM-1, successfully identifying new candidates using as few as half a million cells. This study provides a framework for adopting multiplexed sgRNA strategies to streamline CRISPR screening applications in resource-limited settings.

Humans

The effect of inhibitors of cellular RNA synthesis on stimulation of mouse encephalomyocarditis virus reproduction by poliovirus in HeLa and MIO cells.

Inoculation of HeLa and MIO cells with a guanidine-dependent mutant of poliovirus (gd-polio) in the absence of guanidine resulted in stimulation of mouse encephalomyocarditis (EMC) virus reproduction. No stimulation was found to occur in the presence of actinomycin D, on pre-treatment of the cells with cordycepin, or on their UV irradiation or enucleation. In contrast to HeLa cells, the enhancement of EMC virus reproduction by gd-polio in MIO cells required no current synthesis of cellular RNAs: it occurred in the presence of actinomycin D, upon UV irradiation of the cells or their enucleation. The possible mechanisms of the stimulating effect of poliovirus in HeLa and MIO cells are discussed.

Animals

Interferon action II. Membrane-bound alkaline ribonuclease activity in chick embryo cells manifesting interferon-mediated interference.

Membrane fractions from chick embryo cells manifesting viral interference mediated by interferon or poly(I)-poly(C) contain high levels of an alkaline ribonuclease. Enhanced RNase activity is not observed when inhibitors of cell protein or RNA synthesis are present during interferon treatment, or when heterologous interferon is used. The RNase associated with comparable membrane fractions from cells treated with mock-interferon is about 1/10 as active, and shows qualitative differences. In principle, divergent views of interferon action may be reconciled to a common mode of action by postulating that viral interference results from a newly induced or activated RNase of cellular origin and proper specificity that acts to reduce the accumulation and functional capacity of newly synthesized viral RNAs, particularly mRNA. Previous data in support of interferon's acting to inhibit virion-derived transcription in vivo are now interpreted as demonstrating enhanced degradation of viral transcripts (mRNA).

Animals

UFold-X: an enhanced Dual & Dynamic U-Mamba model for long-range RNA secondary structure prediction.

RNA secondary structure is essential for understanding the functions of non-coding RNAs, ribosomal RNAs, and viral genomes. However, accurate prediction of long RNA structures remains challenging due to complex long-range interactions and the limited availability of long-RNA training data. We present UFold-X, a dual-branch deep learning framework that combines a convolutional encoder for local structure modeling with a Mamba-based Visual State Space Module for capturing long-range dependencies. A dynamic gating mechanism adaptively integrates the two branches according to sequence length. UFold-X was evaluated on multiple benchmark datasets containing RNAs up to 5000 nucleotides. To rigorously assess generalization, we introduced a cross-clan benchmark for long RNAs. Under this stringent setting, UFold-X achieved performance comparable to state-of-the-art classical approaches while achieving the best performance among deep learning-based methods. Additional cross-family and within-family evaluations further demonstrated robust transferability and competitive predictive performance. UFold-X also maintained excellent computational efficiency, requiring only 0.08 s per sequence on average. To assess biological consistency, we developed a SHAPE-based reactivity prediction variant (UFold-X-R) and an integrated metric, the Hybrid Reactivity-Pairing Score (HRPS). UFold-X-R showed strong agreement with experimental icSHAPE data and achieved the highest HRPS among all evaluated methods. A user-friendly web server is available at https://ufold-x.ai4bread.com.

Nucleic Acid Conformation

Epitranscriptomic cytidine methylation of the hepatitis B viral RNA is essential for viral reverse transcription and particle production.

Epitranscriptomic RNA modifications have emerged as important regulators of the fate and function of viral RNAs. One prominent modification, the cytidine methylation 5-methylcytidine (m5C), is found on the RNA of HIV-1, where m5C enhances the translation of HIV-1 RNA. However, whether m5C functionally enhances the RNA of other pathogenic viruses remains elusive. Here, we surveyed a panel of commonly found RNA modifications on the RNA of hepatitis B virus (HBV) and found that HBV RNA is enriched with m5C as well as ten other modifications, at stoichiometries much higher than host messenger RNA (mRNA). Intriguingly, m5C is mostly found on the epsilon hairpin, an RNA element required for viral RNA encapsidation and reverse transcription, with these m5C mainly deposited by the cellular methyltransferase NSUN2. Loss of m5C from HBV RNA due to NSUN2 depletion resulted in a partial decrease in viral core protein (HBc) production, accompanied by a near-complete loss of the reverse transcribed viral DNA. Similarly, mutations introduced to remove the methylated cytidines resulted in a loss of HBc production and reverse transcription. Furthermore, pharmacological disruption of m5C deposition led to a significant decrease in HBV replication. Thus, our data indicate m5C methylations as a critical mediator of the epsilon elements' function in HBV virion production and reverse transcription, suggesting the therapeutic potential of targeting the m5C methyltransfer process on HBV epsilon as an antiviral strategy.

Hepatitis B virus

Molecular determinants of AR-enhancer interaction and cistrome reprogramming in prostate cancer progression.

The androgen receptor (AR) is a key transcription factor in prostate cancer (PCa), whose enhanced and altered functions are known drivers of cancer progression. A key aspect of this is reprogramming of the AR cistrome, which consists of genome-wide enhancer-binding sites through which AR regulates gene expression. The magnitude and biological impact of the AR cistrome are impacted by the AR itself, including the responses to ligand, as well as the organization of the associated DNA response elements, and availability of pioneer factors, cofactors, and noncoding RNAs, all of which contribute to a functional transcription complex. In this review, we will examine, in the context of PCa progression, the factors that affect the binding of AR and its interacting partners at enhancers, with a focus on AR cistrome reprogramming. We also discuss the clinical utility of targeting the AR-enhancer nucleoprotein complex and the potential of using the AR cistrome as a prognostic tool.

Humans

Proteomic profiling identifies miR-423-5p as a modulator of oncogenic metabolism in HCC.

BACKGROUND: Hepatocellular carcinoma (HCC) remains a significant clinical challenge due to limited diagnostic and therapeutic options. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), play key roles in cancer biology. Our previous findings showed that miR-423-5p enhances anti-cancer effects on HCC patients treated with sorafenib by promoting autophagy. Here, we investigated the molecular mechanisms underlying miR-423-5p function through a comprehensive proteomic approach. METHODS: We generated an HCC cell line stably overexpressing miR-423-5p via lentiviral transduction. Total proteins were extracted from SNU-387 cells, enzymatically digested into peptides, and subsequently analysed by liquid chromatography-tandem mass spectrometry (LC-MS/M). Raw spectral data were processed and quantified using MaxQuant. Differentially expressed proteins (DEPs) were defined based on fold-change (|log2FC| &#x2265; 1) and false discovery rate (FDR < 0.05). The full proteomic dataset is available via the ProteomeXchange repository (identifier: PXD064869). Functional enrichment analysis of DEPs were performed using DAVID and Reactome. To assess clinical relevance, predicted and validated miR-423-5p targets were integrated with The Cancer Genome Atlas (TCGA) Liver Hepatocellular Carcinoma (LIHC) dataset using GEPIA platform. Survival analyses were performed using the Kaplan-Meier method. RESULTS: Proteomic profiling identified 698 DEPs in miR-423-5p-overexpressing cells compared to controls with significant enrichment in metabolic pathways, related to purine/pyrimidine metabolism and gluconeogenesis. Integration with bioinformatic predictions and miRTarBase validation identified 43 DEPs as potential direct targets of miR-423-5p. Among these, seven proteins (ACACA, ANKRD52, DVL3, MCM5, MCM7, RRM2, SPNS1, and SRM) were significantly associated with patient prognosis in the TCGA-LIHC cohort. These targets were downregulated in miR-423-5p-overexpressing cells but upregulated in advanced-stage HCC tissues, suggesting a potential role for miR-423-5p in the regulation of HCC pathogenesis. Stage-specific expression analysis showed increased levels from stage I to III, followed by a decline at stage IV. Notably, we experimentally confirmed miR-423-5p-mediated suppression of MCM7, DVL3, IMPDH1, and SRM (SPEE), supporting their functional involvement in HCC progression. CONCLUSION: Overall, our findings support a tumour-suppressive role for miR-423-5p in HCC, mediated by modulation of metabolic pathways and suppression of oncogenic proteins. These results suggest that miR-423-5p and its downstream effectors may serve as promising biomarkers and potential therapeutic targets in HCC. HIGHLIGHTS: miR-423-5p acts as a tumor suppressor in HCC by targeting key nodes of pro-tumorigenic signalling. miR-423-5p significantly altered metabolic pathways, including purine/pyrimidine metabolism and gluconeogenesis. Seven miR-423-5p targets correlate with poor prognosis in TCGA-LIHC patients and are downregulated in miR-423-5p overexpressing HCC cells. miR-423-5p over-expression induces a significant downregulation of MCM7, DVL3, IMPDH1, SPEE in HCC cell models. miR-423-5p limits tumor metabolic plasticity, suggesting therapeutic potential.

MicroRNAs

[Studies on the RNA synthesized in the ovary of immature rats after HCG administration (author's transl)].

Although many researchers have reported that RNA synthesis in the ovary is enhanced by gonadotropin treatment, there are only a few papers concerning the character of newly synthesized RNA after gonadotropin treatment. In this paper, the RNA synthesized in the ovary of immature rats after HCG treatment was qualitatively studied. Immature female Sprague-Dawley rats were administered with 0.3 mc per rat of 3H-uridine at a certain time interval after injection of HCG (10 iu/rat) and the ovaries were subsequently isolated after 15, 30 or 60 minutes. RNA was extracted from the homogenate of the ovaries according to the hot phenol method after Scherrer and Darnell. The 3H-RNA thus extracted was treated with electrophoretically purified DNase to break down and remove DNA that mingled with it. The RNA solution ultimately obtained was analysed on a 3-20% sucrose gradient. The different fractions thus separated were then subjected to measurement of radioactivity and optical density at 260 mmug. The RNA extracted from the ovary of immature untreated rat labeled with 3H-uridine for 15 minutes showed a flat pattern of radioactivity from the top to the bottom fractions with low radioactivity. Otherwise, when labeled for one hour, the RNA showed a pattern of radioactivity like those of optical density at 260 mumu with peaks of r-RNAs and t-RNA. When the ovary was pulse-labeled with 3H-uridine for 15 minutes starting 2 hours after injection of HCG, the RNA with a large S value was synthesized and the pattern of variation in radioactivity was that of rising near the bottom fraction and declining with access to the top fraction. The results obtained by labeling for 15 minutes starting 40 hours after PMS administration were similar to those obtained in immature untreated rats. The patterns of radioactivity in RNA obtained by the labeling for 15 minutes starting 2 hours after HCG and 42 hours after PMS were similar to those starting 2 hours after only HCG injection. The patterns of radioactivity became similar to those of optical density at 260 mmu, when the ovaries were labeled for 30 or 60 minutes. From these results, it was suggested that the newly synthesized RNA 2 hours after HCG was constructed from m-RMA with rapid turn over and precursors of r-RNAs and t-RNA. This RNA synthesis was blocked by pretreatment with actinomycin but not by cycloheximide. From these results, it was suggested that enhancement in RNA polymerase activity or change in template capacity of DNA which would have an effect on RNA synthesis was not based on newly synthesized protein.

Animals

Biomolecular Condensates Integrate Transcriptional and Epigenetic Responses to Hypoxia.

Hypoxia is a defining feature of physiological stress and the core of solid tumors, where aberrant vascularization limits oxygen delivery; cells respond through mechanisms that extend beyond the canonical stabilization of hypoxia-inducible factors (HIFs). Recent studies suggest that hypoxia can promote the formation of specific biomolecular conden-sates, membraneless compartments generated through liquid-liquid phase separation in which regulatory proteins and RNAs become locally enriched at genomic regions, while chromatin mainly serves as an organizational scaffold. Transcription factors, the coacti-vators p300/CBP, Mediator, and BRD4, chromatin-modifying enzymes, and architectural RNAs such as NEAT1 and MALAT1 partition into these compartments, and their con-densation can help reorganize local chromatin structure and enhancer-promoter interac-tions. Because molecular oxygen is a shared co-substrate for the Jumonji-C histone demethylases and the ten-eleven translocation (TET) DNA dioxygenases, hypoxia reshapes histone methylation and DNA methylation in parallel, and readers that bridge these marks, including UHRF1, may participate in condensate-associated chromatin regulation. Hypoxia-driven condensation of ZHX2 rewires enhancer-promoter contacts and higher-order genome architecture, influencing cell identity, stemness, and metastatic potential, and Polycomb condensates represent another candidate epigenetic compartment that may be influenced by hypoxic signaling. These processes may be particularly important in cancer, where chronic hypoxia provides a sustained stimulus for condensate formation and epigenetic remodeling. Together, these findings support a model in which phase separation and epigenetic reprogramming are not separate layers but one integrated response to low oxygen, offering opportunities to target maladaptive condensates in disease.

Epigenesis, Genetic

The emerging impact of CRISPR and gene editing on global crop improvement.

The advent of CRISPR-based genome editing has revolutionized crop improvement, offering unprecedented precision and efficiency in modifying key agronomic traits. This review comprehensively examines the mechanisms, applications, and future potential of CRISPR technology in enhancing global crop production. CRISPR-Cas systems, originally identified as adaptive immune mechanisms in bacteria and archaea, have been repurposed for targeted genome editing in plants. The CRISPR-Cas9 system, in particular, has emerged as a powerful tool for introducing site-specific double-strand breaks, enabling precise genetic modifications. The three-stage process of adaptation, expression, and interference underlies the CRISPR mechanism, with guide RNAs directing Cas endonucleases to specific genomic loci. Advances in CRISPR technology have expanded its applications beyond gene knockouts, encompassing base editing, prime editing, and epigenome editing. These innovations have facilitated the development of crops with enhanced yield, stress tolerance, disease resistance, nutritional content, and post-harvest quality. However, challenges related to off-target effects, regulatory hurdles, ethical concerns, and public acceptance must be addressed to fully harness the potential of CRISPR in agriculture. Integration of CRISPR with other cutting-edge technologies, such as synthetic biology, artificial intelligence, and high-throughput phenotyping, holds immense promise for accelerating crop improvement efforts. As research continues to refine CRISPR tools and expand their applicability across diverse plant species, this transformative technology is poised to play a pivotal role in shaping a sustainable, resilient, and productive global food system for future generations.

Gene Editing

Globin mRNAs are primers for the transcription of influenza viral RNA in vitro.

Because influenza viral RNA transcription in vitro is greatly enhanced by the addition of a primer dinucleotide, ApG or GpG, we have proposed that viral RNA transcription in vivo requires initiation by primer RNAs synthesized by the host cell, specifically by RNA polymerase II, thereby explaining the alpha-amanitin sensitivity of viral RNA transcription in vivo. Here, we identify such primer RNAs, initially in reticulocyte extracts, where they are shown to be globin mRNAs. Purified globin mRNAs very effectively stimulated viral RNA transcription in vitro, and the resulting transcripts directed the synthesis of all the nonglycosylated virus-specific proteins in micrococcal nuclease-treated L cell extracts. The viral RNA transcripts synthesized in vitro primed by ApG also directed the synthesis of the nonglycosylated virus-specific proteins, but the globin mRNA-primed transcripts were translated about 3 times more efficiently. The translation of the globin mRNA-primed, but not the ApG-primed, viral RNA transcripts was inhibited by 7-methylguanosine 5'-phosphate in the presence of S-adenosylhomocysteine, suggesting that the globin mRNA-primed transcripts contained a 5'-terminal methylated cap structure. We propose that this cap was transferred from the globin mRNA primer to the newly synthesized viral RNA transcripts, because no detectable de novo synthesis of a methylated cap occurred during globin mRNA-primed viral RNA transcription. Preliminary experiments indicate that other purified eukaryotic mRNAs also stimulate influenza viral RNA transcription in vitro.

Globins

Interactions of plant viral RNAs and tRNA nucleotidyl transferase.

Ribonucleic acid from TMV and BMV can accept AMP and CMP when digested with VPD. This incorporation is catalyzed by E. coli and yeast tRNA nucleotidyl transferases. Complex formation is obtained between TYMV RNA and tRNA nucleotidyl transferase in sucrose gradients while TMV and BMV RNAs failed to form a complex in the same conditions. The affinity of the enzyme for viral RNAs is lower than the affinity for tRNA as shown by complex formation on nitrocellulose filters and competition with tRNA. Coat protein from TMV particles enhances AMP and CMP incorporation onto tRNA catalyzed by the E. coli tRNA nucleotidyl transferase.

Adenosine Monophosphate