The selective interruption of nucleolar RNA synthesis in HeLa cells by cordycepin

piRNA generation is associated with the pioneer round of translation in stem cells

Much insight has been gained on how stem cells maintain genomic integrity, but less attention has been paid to how they maintain their transcriptome. Here, we report that the PIWI protein SMEDWI-1 plays a role in the filtering of dysfunctional transcripts from the transcriptome of planarian stem cells. SMEDWI-1 accomplishes this through association with the ribosomes during the pioneer round of translation, and processing of poorly translated transcripts into piRNAs. This results in the removal of such transcripts from the cytoplasmic pool and at the same time creates a dynamic pool of small RNAs for post-transcriptional surveillance through the piRNA pathway. Loss of SMEDWI-1 results in elevated levels of several non-coding transcripts, including rRNAs, snRNAs and pseudogene mRNAs, while reducing levels of several coding transcripts. In the absence of SMEDWI-1, stem cell colonies are delayed in their expansion and a higher fraction of descendants exit the stem cell state, indicating that this transcriptomic sanitation mediated by SMEDWI-1 is essential to maintain stem cell health. This study presents a new model for the function of PIWI proteins in stem cell maintenance, that complements their role in transposon repression, and proposes a new biogenesis pathway for piRNAs in stem cells.

Effect of Cordyceps militaris Hot Water Extract on Immunomodulation-associated Gene Expression in Broilers, Gallus gallus

Cordyceps militaris is a well-known Chinese medicinal fungus that has been used as a nutraceutical food in several Asian countries. Cordycepin (3′-deoxyadenosine), a secondary metabolite produced from Cordyceps militaris, has been demonstrated to exert a wide spectrum of pharmacological activities, such as anti-microbial and antitumor activities. However, the effect of cordycepin on immunomodulation in broilers is poorly investigated. In the current study, we investigated the effect of cordycepin (9.69, 19.38, and 38.76 mg) from Cordyceps militaris hot water extract (CMHW) on growth performance and immunocompetence in broilers. Results showed that CMHW significantly decreased inducible nitric oxide synthase (iNOS) mRNA levels in the bursa of Fabricius after 4 weeks of feeding (P<0.05). CMHW treatment reduced cyclooxygenase-2 (COX-2) mRNA levels in the spleen and bursa of Fabricius after 4 weeks of feeding (P<0.05). Supplementation of CMHW for 3 days after vaccination reduced iNOS mRNA level in the spleen of 14 and 28 day-old broilers (P<0.05). Prior to vaccination, CMHW pretreatment significantly down-regulated COX-2 mRNA levels in the spleen and bursa of Fabricius of 14-day-old broilers (P<0.05). Furthermore, CMHW significantly reduced lipopolysaccharide (LPS)-induced iNOS and COX-2 mRNA levels in the spleen and bursa of Fabricius (P<0.05). CMHW treatment attenuated LPS-induced IFN-γ expression in the spleen and bursa of Fabricius, whereas CMHW induced IL-4 expression in these organs in response to LPS challenge (P<0.05). Taken together, these observations demonstrate that CMHW exerts an immunomodulatory role in broilers. CMHW is a potential novel feed additive with applications in inflammation-related diseases and bacterial infection in broilers.

Secondary metabolites (SMs) of Isaria cicadae and Isaria tenuipes

Both Isaria cicadae and Isaria tenuipes are important entomopathogenic fungi used in health foods and traditional herbal medicines in East Asia. However, the safety concerns for both fungal species have been attracting significant attention. Thus, surveying their secondary metabolites (SMs) will be beneficial to improving the safety of their fungal products. In the case of I. cicadae, its SMs mainly include nucleosides, amino acids, beauvericins, myriocin, and oosporein. In contrast, trichothecene derivatives, isariotins, cyclopenta benzopyrans and PKs, are found in the case of I. tenuipes. Among them, beauvericins, myriocin, oosporein and many trichothecene derivatives are toxic compounds. The toxicity and side effects of the fungal products may be related to these SMs. Thus, to ensure the safety of fungal products, the residues standards of SMs need to be reported. Furthermore, methods for the detection of their SMs and biological identification of their strains must be considered. This review gives new insight into the secondary metabolites of medical and edible fungi.

Direct and Indirect Effects on Viral Translation and RNA Replication Are Required for AUF1 Restriction of Enterovirus Infections in Human Cells

Picornaviruses primarily infect the gastrointestinal or upper respiratory tracts of humans and animals and may disseminate to tissues of the central nervous system, heart, skin, liver, or pancreas. Many common human pathogens belong to the Picornaviridae family, which includes viruses known to cause paralytic poliomyelitis (poliovirus); myocarditis (coxsackievirus B3 [CVB3]); the common cold (human rhinovirus [HRV]); and hand, foot, and mouth disease (enterovirus 71 [EV71]), among other illnesses. There are no specific treatments for infection, and vaccines exist for only two picornaviruses: poliovirus and hepatitis A virus. Given the worldwide distribution and prevalence of picornaviruses, it is important to gain insight into the host mechanisms used to restrict infection. Other than proteins involved in the innate immune response, few host factors have been identified that restrict picornavirus replication. The work presented here seeks to define the mechanism of action for the host restriction factor AUF1 during infection by poliovirus and CVB3.

The cellular mRNA decay protein AUF1 acts as a restriction factor during infection by picornaviruses, including poliovirus, coxsackievirus, and human rhinovirus. AUF1 relocalizes from the nucleus to the cytoplasm during infection by these viruses due to the disruption of nucleocytoplasmic trafficking by viral proteinases. Previous studies have demonstrated that AUF1 binds to poliovirus and coxsackievirus B3 (CVB3) RNA during infection, with binding shown to occur within the internal ribosome entry site (IRES) of the 5′ noncoding region (NCR) or the 3′ NCR, respectively. Binding to different sites within the viral RNA suggests that AUF1 may negatively regulate infection by these viruses using different mechanisms. The work presented here addresses the mechanism of AUF1 inhibition of the replication of poliovirus and CVB3. We demonstrate that AUF1 knockdown in human cells results in increased viral translation, RNA synthesis, and virus production. AUF1 is shown to negatively regulate translation of a poliovirus and CVB3 IRES reporter RNA during infection but not in uninfected cells. We found that this inhibitory activity is not mediated through destabilization of viral genomic RNA; however, it does require virus-induced relocalization of AUF1 from the nucleus to the cytoplasm during the early phases of infection. Our findings suggest that AUF1 restriction of poliovirus and CVB3 replication uses a common mechanism through the viral IRES, which is distinct from the canonical role that AUF1 plays in regulated mRNA decay in uninfected host cells.

Separation of cordycepin from Cordyceps militaris fermentation supernatant using preparative HPLC and evaluation of its antibacterial activity as an NAD+-dependent DNA ligase inhibitor

Cordycepin exhibits various bio-activities, including anticancer, antibacterial, antiviral and immune regulation activities, and is a significant focus of research. However, the preparation of high-purity cordycepin remains challenging. Also, the molecular target with which cordycepin interacts to cause an antibacterial effect remains unknown. In the present study, cordycepin was prepared by preparative high-performance liquid chromatography (prep-HPLC) and the purity obtained was 99.6%, indicating that this technique may be useful for the large-scale isolation of cordycepin in the future. The results of computational molecular docking analysis indicated that the interaction energy between cordycepin and NAD+-dependent DNA ligase (LigA) was lower than that between cordycepin and other common antibacterial targets. The highly pure cordycepin obtained by prep-HPLC demonstrated inhibitory activity against LigA from various bacteria in vitro. In conclusion, cordycepin may be useful as a broad-spectrum antibiotic targeting LigA in various bacteria.

Cordycepin induces apoptosis and autophagy in human neuroblastoma SK-N-SH and BE(2)-M17 cells

Cordycepin, also termed 3'-deoxyadenosine, is a derivative of the nucleoside adenosine that represents a potential novel class of anticancer drugs targeting the 3' untranslated region of RNAs. Cordycepin has been reported to induce apoptosis in certain cancer cell lines, but the effects of cordycepin on human neuroblastoma cells have not been studied. In the present study, an MTT assay revealed that cordycepin inhibits the viability of neuroblastoma SK-N-SH and BE(2)-M17 cells in a dose-dependent manner. In addition, cordycepin increases the early-apoptotic cell population of SK-N-SH cells, as determined by fluorescence-activated cell sorting analysis. The induction of apoptosis in neuroblastoma cells by cordycepin was further confirmed by western blotting, which revealed cleavage of caspase-3 and poly(adenosine diphosphate-ribose) polymerase 1 in the SK-N-SH and BE(2)-M17 cells. Cordycepin also induced the formation of a punctate pattern of light-chain 3 (LC3)-associated green fluorescence in the SK-N-SH cells transfected with a pEGFP-LC3 vector. Furthermore, western blotting revealed cleavage of LC3 A/B in cordycepin-treated neuroblastoma SK-N-SH cells. Taken together, the results indicate that cordycepin significantly increases apoptosis and autophagy in neuroblastoma cells, and may therefore be a drug candidate for neuroblastoma therapy, but requires additional evaluation.

Cordyceptin induces apoptosis through repressing hTERT expression and inducing extranuclear export of hTERT

Cordycepin is an adenosine analog originally extracted from Cordyceps militaris that possesses many pharmacological effects including immune activation and antioxidant and antitumor effects. However, the underlying relationship between apoptosis and telomerase activity in response to cordycepin exposure has not been investigated. In this study, we found that cordycepin-induced apoptosis of human leukemia cells (H937 and THP-1 cells) was associated with inactivation of telomerase and downregulation of human telomerase reverse transcriptase (hTERT) as well as the transcription factors c-Myc and Sp1, which are required for basal transcription from the hTERT gene promoter. Cordycepin also attenuated the activation of phosphoinositide-3-kinase (PI3K)/Akt signaling, thereby reducing phosphorylation and nuclear translocation of hTERT. We further showed that the PI3K inhibitor LY29004 significantly decreased telomerase activity in cordycepin-treated cells and increased cordycepin-induced cell death. These findings demonstrate that cordycepin is cytotoxic to human leukemia cells and suppresses telomerase activity through transcriptional and post-translational suppression of hTERT by inactivating the PI3K/Akt signaling pathway.

HYPER RECOMBINATION1 of the THO/TREX complex plays a role in controlling transcription of the REVERSION-TO-ETHYLENE SENSITIVITY1 gene in Arabidopsis

Arabidopsis REVERSION-TO-ETHYLENE SENSITIVITY1 (RTE1) represses ethylene hormone responses by promoting ethylene receptor ETHYLENE RESPONSE1 (ETR1) signaling, which negatively regulates ethylene responses. To investigate the regulation of RTE1, we performed a genetic screening for mutations that suppress ethylene insensitivity conferred by RTE1 overexpression in Arabidopsis. We isolated HYPER RECOMBINATION1 (HPR1), which is required for RTE1 overexpressor (RTE1ox) ethylene insensitivity at the seedling but not adult stage. HPR1 is a component of the THO complex, which, with other proteins, forms the TRanscription EXport (TREX) complex. In yeast, Drosophila, and humans, the THO/TREX complex is involved in transcription elongation and nucleocytoplasmic RNA export, but its role in plants is to be fully determined. We investigated how HPR1 is involved in RTE1ox ethylene insensitivity in Arabidopsis. The hpr1-5 mutation may affect nucleocytoplasmic mRNA export, as revealed by in vivo hybridization of fluorescein-labeled oligo(dT)45 with unidentified mRNA in the nucleus. The hpr1-5 mutation reduced the total and nuclear RTE1 transcript levels to a similar extent, and RTE1 transcript reduction rate was not affected by hpr1-5 with cordycepin treatment, which prematurely terminates transcription. The defect in the THO-interacting TEX1 protein of TREX but not the mRNA export factor SAC3B also reduced the total and nuclear RTE1 levels. SERINE-ARGININE-RICH (SR) proteins are involved mRNA splicing, and we found that SR protein SR33 co-localized with HPR1 in nuclear speckles, which agreed with the association of human TREX with the splicing machinery. We reveal a role for HPR1 in RTE1 expression during transcription elongation and less likely during export. Gene expression involved in ethylene signaling suppression was not reduced by the hpr1-5 mutation, which indicates selectivity of HPR1 for RTE1 expression affecting the consequent ethylene response. Thus, components of the THO/TREX complex appear to have specific roles in the transcription or export of selected genes.

Anti-inflammatory effects of cordycepin in lipopolysaccharide-stimulated RAW 264.7 macrophages through Toll-like receptor 4-mediated suppression of mitogen-activated protein kinases and NF-κB signaling pathways

Cordycepin is the main functional component of the Cordyceps species, which has been widely used in traditional Oriental medicine. This compound possesses many pharmacological properties, such as an ability to enhance immune function, as well as antioxidant, antiaging, and anticancer effects. In the present study, we investigated the anti-inflammatory effects of cordycepin using a murine macrophage RAW 264.7 cell model. Our data demonstrated that cordycepin suppressed production of proinflammatory mediators such as nitric oxide (NO) and prostaglandin E₂ by inhibiting inducible NO synthase and cyclooxygenase-2 gene expression. Cordycepin also inhibited the release of proinflammatory cytokines, including tumor necrosis factor-alpha and interleukin-1-beta, through downregulation of respective mRNA expression. In addition, pretreatment with cordycepin significantly inhibited lipopolysaccharide (LPS)-induced phosphorylation of mitogen-activating protein kinases and attenuated nuclear translocation of NF-κB by LPS, which was associated with abrogation of inhibitor kappa B-alpha degradation. Furthermore, cordycepin potently inhibited the binding of LPS to macrophages and LPS-induced Toll-like receptor 4 and myeloid differentiation factor 88 expression. Taken together, the results suggest that the inhibitory effects of cordycepin on LPS-stimulated inflammatory responses in RAW 264.7 macrophages are associated with suppression of mitogen-activating protein kinases and activation of NF-κB by inhibition of the Toll-like receptor 4 signaling pathway.

High-resolution analysis of gene activity during the Xenopus mid-blastula transition

The Xenopus mid-blastula transition (MBT) marks the onset of large-scale zygotic transcription, as well as an increase in cell cycle length and a loss of synchronous cell divisions. Little is known about what triggers the activation of transcription or how newly expressed genes interact with each other. Here, we use high-resolution expression profiling to identify three waves of gene activity: a post-fertilisation wave involving polyadenylation of maternal transcripts; a broad wave of zygotic transcription detectable as early as the seventh cleavage and extending beyond the MBT at the twelfth cleavage; and a shorter post-MBT wave of transcription that becomes apparent as development proceeds. Our studies have also allowed us to define a set of maternal mRNAs that are deadenylated shortly after fertilisation, and are likely to be degraded thereafter. Experimental analysis indicates that the polyadenylation of maternal transcripts is necessary for the establishment of proper levels of zygotic transcription at the MBT, and that genes activated in the second wave of expression, including Brachyury and Mixer, contribute to the regulation of genes expressed in the third. Together, our high-resolution time series and experimental studies have yielded a deeper understanding of the temporal organisation of gene regulatory networks in the early Xenopus embryo.

Transcriptome analysis of the Ophiocordyceps sinensis fruiting body reveals putative genes involved in fruiting body development and cordycepin biosynthesis

Ophiocordyceps sinensis is a highly valuable and popular medicinal fungus used as a tonic and roborant for thousands of years in traditional Asian medicine. However, unsustainable harvesting practices have endangered this species and very little is known about its developmental programming, its biochemistry and genetics. To begin to address this, the transcriptome of the medicinal O. sinensis fruiting body was analyzed by high-throughput. In this O. sinensis 454-EST dataset, four mating type genes and 121 genes that may be involved in fruiting body development, especially in signal transduction and transcription regulation, were discovered. Moreover, a model was developed for the synthesis of the primary medicinal compound, cordycepin, and the putative biosynthetic enzymes identified. This transcriptome dataset provides a significant new resource for gene discovery in O. sinensis and dissection of its valuable biosynthetic and developmental pathways.

Evidence That Naturopathic Therapy Including Cordyceps sinensis Prolongs Survival of Patients With Hepatocellular Carcinoma

Hypothesis. Naturopathic treatment will benefit patients with hepatocellular carcinoma (HCC). Study design. Retrospective analysis of case series of HCC patients treated with naturopathic agents. Methods. HCC was diagnosed by dynamic computed tomography (CT) imaging and α-fetoprotein (AFP) or PIVKA II, or by histology. Tumor staging was determined by CT. A modified Childs–Pugh scoring was used to assess liver disease. Patients were treated with orally administered combinations of 12 naturopathic agents. Patients were monitored clinically and by CT tumor imaging, serial tumor markers, and liver function tests. Results. Patient characteristics: 101 patients with HCC (67 men and 34 women, age 67.2 ± 8.8 years) were treated for a median of 13.4 months (range 0.8-100.8). Of these 84% had cirrhosis, 63% had hepatitis C virus, 18% had hepatitis B virus, 1% had both, and 9% had metastatic disease. Median modified Childs–Pugh score was 6 (range 3-13). Barcelona Clinic Liver Cancer tumor stages of 0, A, B, C, and D were found in 36%, 25%, 20%, 14%, and 6%, respectively. Median AFP was 40 (range 0-311,000). Median PIVKA II was 59 (0–378,000). Previous treatment was included none (27%), resection with relapse (20%), transarterial chemoembolization (50%), radiofrequency ablation (28%), percutaneous ethanol injection therapy (15%), chemotherapy (14%). Outcomes: Initial treatment was with 2.6 ± 0.8 agents (range 2-4). Overall, patients were treated with 3.7 ± 1.2 agents (range 2-7). There was a significant correlation between number of agents administered and survival ( P < .0001). Patients treated with ≥4 agents survived significantly longer than patients treated with ≤3 agents (40.2 vs 6.4 months, P < .0001). This difference could not be attributed to statistically significant differences in severity of liver disease or tumor stage, delay in treatment, previous treatment, concurrent nondrug treatment, or censoring effects. The greatest effect was seen in patients treated with at least 4 agents that included Cordyceps sinensis. This prolonged survival was without toxic side effects and appeared to potentiate the survival benefit of conventional therapy. Conclusion. Treatment of HCC with a regimen of ≥4 agents prepared from natural products was associated with prolonged survival in a substantial portion of patients. The data provide level II evidence for the efficacy of naturopathic therapy in HCC.

Frog virus 3 replication: induction and intracellular distribution of polypeptides in infected cells

The synthesis of the polypeptides induced in frog virus 3-infected cells was analyzed by high-resolution sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radiolabeled cell extracts. Purified frog virus 3 contained 22 polypeptides, with molecular weights in the range 9 x 10(3) to 114 x 10(3). All of the structural and an additional seven nonstructural polypeptides were detected in infected cell lysates. The following three classes of induced polypeptides (under temporal control) were observed in BHK cells: at 2 h, four alpha polypeptides; at 4 h, 13 beta polypeptides; and at 6 h, the remaining 12 gamma polypeptides. The total molecular weight of the infected cell-specific polypeptides (ICPs) was approximately 1.5 x 10(6), which accounts for about 30% of the coding capacity of the viral genome. At least 10 of the induced polypeptides were phosphorylated, but none was glycosylated or sulfated. No evidence for posttranslation cleavage of polypeptides in pulse-chase and inhibition experiments was obtained. The synthesis of gamma polypeptides was not detected in the presence of the viral DNA replication inhibitors cytosine arabinoside and hydroxyurea, but halogenated nucleotides apparently had no effect. These results suggest that alpha and beta polypeptides are "early" events and that detectable gamma polypeptide synthesis is dependent on the production of progeny viral DNA. The regulation of frog virus 3-induced polypeptide synthesis in infected BHK cells was examined by using inhibitors of protein and RNA synthesis and amino acid analogs. These experiments confirmed the existence of three sequentially synthesized, coordinately regulated classes of polypeptides, designated alpha, beta, and gamma. The requirements for the synthesis of each class were as follows: (i) alpha polypeptides did not require previous cell protein synthesis; (ii) beta polypeptides required a prescribed period of alpha polypeptide synthesis and new mRNA synthesis; and (iii) gamma polypeptides required prior synthesis of functional beta polypeptides and new mRNA synthesis. alpha polypeptide synthesis was controlled by beta and gamma polypeptides, and alpha and beta polypeptides were involved in the suppression of host cell polypeptide synthesis. Indirect evidence was obtained for the temporal regulation of frog virus 3 transcription. The intracellular distribution of virus-induced polypeptides in cells infected with frog virus 3 was investigated by using standard cell fractionation techniques. Most of the 29 induced polypeptides were bound to structures within the nucleus, and only two ICPs were not associated with purified nuclei. When isolated nuclei were incubated in an infected cell cytoplasm preparation, all of the nuclear ICPs were incorporated in vitro. All of the ICPs were associated with ribosomal and rough endoplasmic reticulum fractions of infected cells, and a number of ICPs were found on smooth intracellular membranes. Most of the ICPs were also associated with purified plasma membranes of infected cells, and one polypeptide (ICP 58) was highly enriched in the plasma membrane compared with whole cell extracts or purified frog virus 3.

Pharmacokinetics of adenosine and cordycepin, a bioactive constituent of Cordyceps sinensis in rat

Cordycepin is a bioactive constituent of Cordyceps sinensis that has been shown to regulate homeostatic function. As an adenosine analogue, it is possible cordycepin goes through a similar metabolic pathway to that of adenosine. To investigate this hypothesis, a sensitive liquid chromatography with photodiode-array detector (HPLC-PDA) coupled to a microdialysis sampling system was developed to monitor cordycepin and adenosine in rat blood and liver. Other endogenous nucleosides were simultaneously measured to further understand the downstream metabolic pathway. The experiments were divided into six parallel groups for drug administration: (1) normal saline vehicle, (2) adenosine, (3) cordycepin, (4) normal saline + erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; a potent adenosine deaminase inhibitor), (5) adenosine + EHNA, and (6) cordycepin + EHNA. The pharmacokinetic results suggest that the levels of both adenosine and cordycepin decreased rapidly in blood around 30 min after drug administration. When adenosine was given, the concentrations of adenosine metabolites, hypoxanthinosine and hypoxanthine, increased in rat blood. This phenomenon was inhibited by EHNA pretreatment. An unidentified peak was observed in the blood and liver samples after cordycepin administration. The decline of this unidentified peak paralleled the decreased of the concentration of cordycepin, and it was not observed in the presence of the adenosine deaminase inhibitor. It is concluded that adenosine and cordycepin had short elimination half-lives and high rates of clearance and their biotransformation was suppressed by EHNA.

Subnuclear compartmentalization and function of actin and nuclear myosin I in plants

Actins are highly conserved proteins that serve as the basic building blocks of cytoskeletal microfilaments. In animal cells, specific nuclear actin adopts unconventional conformations that are involved in multiple nuclear functions and that associate with nuclear actin binding proteins. However, there is practically no information available about nuclear actin in plants. Indeed, actin has not been detected in the nuclear proteomes of many plants, and orthologs of the main structural nuclear actin-binding proteins have yet to be identified. Here, we have investigated the characteristics, intranuclear compartmentalization, and function of actin in isolated Allium cepa nuclei as well as that of its motor protein nuclear myosin I (NMI). Using conformation-specific antibodies for nuclear actin isoforms, ss-actin, and NMI, the distribution of these proteins was studied in Western blots and by immunocytochemistry. Moreover, the participation of nuclear actin in transcription was analyzed in run on in situ assays and inhibition of RNA polymerases I and II. We show that actin isoforms with distinct solubilities are present in onion nuclei with a consistent subnuclear compartmentalization. Actin and NMI are highly enriched in foci that are similar to transcription foci, although actin is also distributed diffusely in the nucleus and nucleolus as well as accumulating in a subset of the Cajal bodies. Immunogold labeling identified both proteins in the nuclear transcription subdomains and in other subnuclear compartments. In addition, actin and NMI were diffusely distributed in the nuclear matrix.

Rapid, diffusional shuttling of poly(A) RNA between nuclear speckles and the nucleoplasm

Speckles are nuclear bodies that contain pre-mRNA splicing factors and polyadenylated RNA. Because nuclear poly(A) RNA consists of both mRNA transcripts and nucleus-restricted RNAs, we tested whether poly(A) RNA in speckles is dynamic or rather an immobile, perhaps structural, component. Fluorescein-labeled oligo(dT) was introduced into HeLa cells stably expressing a red fluorescent protein chimera of the splicing factor SC35 and allowed to hybridize. Fluorescence correlation spectroscopy (FCS) showed that the mobility of the tagged poly(A) RNA was virtually identical in both speckles and at random nucleoplasmic sites. This same result was observed in photoactivation-tracking studies in which caged fluorescein-labeled oligo(dT) was used as hybridization probe, and the rate of movement away from either a speckle or nucleoplasmic site was monitored using digital imaging microscopy after photoactivation. Furthermore, the tagged poly(A) RNA was observed to rapidly distribute throughout the entire nucleoplasm and other speckles, regardless of whether the tracking observations were initiated in a speckle or the nucleoplasm. Finally, in both FCS and photoactivation-tracking studies, a temperature reduction from 37 to 22 degrees C had no discernible effect on the behavior of poly(A) RNA in either speckles or the nucleoplasm, strongly suggesting that its movement in and out of speckles does not require metabolic energy.

Effects of polyadenylation inhibition on meiosis progression in relation to the polyadenylation status of cyclins A2 and B1 during in vitro maturation of bovine oocytes

The control of protein synthesis during maturation in oocytes is mainly exerted through cytoplasmic polyadenylation of stored mRNAs. We first analyzed the polyadenylation status of cyclins A2 and B1 during in vitro maturation (IVM) of bovine oocytes, using Rapid Amplification of cDNA Ends-Polyadenylation Technique (RACE-PAT). An inconstant elongation of the poly(A) tail was observed for cyclin A2 transcripts after maturation, while a constant lengthening was observed for cyclin B1, occurring during the first 12 hr of incubation. We then evaluated the effects of the polyadenylation inhibitor 3'-deoxyadenosine (3'-dA), on polyadenylation and nuclear maturation. The presence of 0.02 mM 3'-dA during the whole incubation period or from 6 hr after its beginning completely prevented meiosis progression in 100% of the oocytes. Polyadenylation of cyclin B1 was also completely prevented when 3'-dA was added at 0 hr, and greatly reduced when added at 6 hr. When 3'-dA was added at 12 hr, around metaphase I (MI), 46.9% of the oocytes have reached metaphase II (MII, vs. 78.8% in the control group) at 24 hr. The use of the same concentration of 3'-deoxyguanosine (3'-dG), that impairs transcription but not polyadenylation, did not affect cyclins polyadenylation, nor nuclear maturation, whatever was the timing of addition. These results suggest that the polyadenylation of cyclin B1 could be related to the first peak of activity of MPF, occurring around MI (10-12 hr after the onset of the maturation period). They also show that, in our culture conditions, inhibition of polyadenylation prevents meiosis progression, especially up to the MI stage, while inhibition of transcription does not.

In vitro antimalarial activity of nucleic acid precursor analogues in the simian malaria Plasmodium knowlesi

Analogues of nucleic acid precursors were screened for antimalarial activity in Plasmodium knowlesi by using an in vitro culture system. Activity was assessed by the degree of inhibition of incorporation of l-[methyl-(14)C]methionine into protein and of [8-(14)C]adenosine and [6-(14)C]orotic acid into ribonucleic acid and deoxyribonucleic acid. The incorporation of adenosine or orotic acid was effectively inhibited by many of the compounds, including 3' analogues of purine nucleosides, many of the 6-position analogues of purine bases and nucleosides, and 5-position analogues of orotic acid. Only a few compounds inhibited methionine incorporation into protein, and in each instance adenosine or orotic acid incorporation also was inhibited. Some compounds inhibited adenosine or orotic acid incorporation into both ribonucleic acid and deoxyribonucleic, whereas other analogues inhibited incorporation into one nucleic acid only. The qualitative and quantitative differences suggest that this experimental system may be appropriate for investigation of metabolic pathways of the malaria parasite, as well as for demonstration of antimalarial activity of candidate antimalaria drugs.

Acquisition of transcriptional competence in the 1-cell mouse embryo: requirement for recruitment of maternal mRNAs

We previously suggested that the transcriptional machinery is rate-limiting for genome activation in the preimplantation mouse embryo (Aoki et al., 1997: Dev Biol 181:296-307), suggesting that genome activation requires the synthesis of some proteins following fertilization. To test this hypothesis, transcriptional activity was measured in 1-cell embryos in which protein synthesis was inhibited by cycloheximide from the time shortly after insemination. Transcription in both the male and female pronuclei, as assessed by BrUTP incorporation, was markedly inhibited when assayed 14 hr post-insemination. This result suggested that newly synthesized proteins derived from maternally recruited mRNA, and not maternally derived proteins that were post-translationally modified following fertilization/egg activation, were critical for the acquisition of transcriptional competence. To test this hypothesis, mobilization of maternally recruited mRNAs was inhibited by treating the embryos with 3'-deoxyadenosine (3'-dA), which prevents polyadenylation of mRNA. The results demonstrated that the transcriptional activity was markedly decreased in the embryos cultured with 2 mM 3'-dA, whereas 3'-deoxyguanosine had little inhibitory effect, and suggest that recruitment of maternal mRNAs is essential for acquisition of transcriptional competence.

Three-dimensional organization of active rRNA genes within the nucleolus

In this work, we have localized transcribing rRNA genes at the ultrastructural level and described their three-dimensional organization within the nucleolus by electron tomography. Isolated nucleoli, which exhibit a reduced transcriptional rate, were used to determine the sites of initial BrUTP incorporation (i.e. rRNA synthesis by the transcriptional machinery). Using pulse-chase experiments with BrUTP and an elongation inhibitor,cordycepin, it was possible to precisely localize the initial sites of BrUTP incorporation. Our data show that BrUTP incorporation initially takes place in the fibrillar centers and that elongating rRNAs rapidly enter the surrounding dense fibrillar component. Furthermore, we investigated the spatial arrangement of RNA polymerase I molecules within the whole volume of the fibrillar centers. Electron tomography was performed on thick sections of cells that had been labeled with anti-RNA polymerase I antibodies prior to embedding. Detailed tomographic analyses revealed that RNA polymerase I molecules are mainly localized within discrete clusters. In each of them, RNA polymerase I molecules were grouped as several coils, 60 nm in diameter. Overall, these findings have allowed us to propose a model for the three-dimensional organization of transcribing rDNA genes within the nucleolus.

Alterations in the maturation and structure of ribosomal precursor RNA in Novikoff hepatoma cells induced by 5-fluorocytidine

The effects of 5-fluorocytidine on ribosomal RNA maturation and structure in Novikoff hepatoma cells were investigated. Like other nucleic acid base analogues that are incorporated into RNA, this compound inhibits maturation of the 45S ribosomal RNA precursor. The 45S RNA precursor produced in the presence of 5-fluorocytidine has an abnormal electrophoretic mobility compared with that of the control precursor under nondenaturing conditions, but the two have identical mobilities under denaturing conditions. Under the conditions of these experiments, 5-fluorocytidine inhibited cellular protein synthesis only slightly, whereas equimolar concentrations of 5-azacytidine resulted in nearly 75% inhibition of this process. Despite this difference in the effects of the two analogues as well as the greater chemical lability of the 5-azacytidine, their effects on ribosomal RNA maturation are identical.

Posttranscriptional regulation of cyclin A1 and cyclin A2 during mouse oocyte meiotic maturation and preimplantation development

A shift from a meiotic cell cycle to a mitotic cell cycle occurs following fertilization. The molecular basis for this transition, however, is poorly understood. Although cyclin A1 is proposed to regulate M phase in the meiotic cell cycle, and cyclin A2 is proposed to regulate S and M phases in the mitotic cell cycle, little is known about changes in the expression levels of cyclin A1 and A2 during meiotic and mitotic cell cycles in mammalian oocytes. We report that the mRNA levels of both cyclins A1 and A2 decrease during oocyte maturation. The amount of cyclin A1 mRNA then increases between the one-cell and blastocyst stages, whereas that of cyclin A2 remains relatively constant. The amount of cyclin A1 protein declines during maturation and is not readily detected from the two-cell to the blastocyst stage. In contrast, cyclin A2 is not readily detected in the oocyte and metaphase II-arrested egg but is detected following fertilization and throughout the subsequent stages of preimplantation development. The appearance of cyclin A2 protein following fertilization positively correlates with an increase in the size of the mRNA. This increase, as well as the increase in the amount of cyclin A2 protein, is prevented by 3'-deoxyadenosine (3'-dA), an inhibitor of polyadenylation. Consistent with a role for cyclin A2 in regulating the G1/S transition, 3'-dA also inhibits DNA replication in treated one-cell embryos. These results suggest that regulation of expression of cyclins A1 and A2 is under posttranscriptional regulation and that the observed changes in their expression may be involved in the transformation of a meiotic cell cycle to a mitotic cell cycle following fertilization.

Ara-ATP impairs 3'-end processing of pre-mRNAs by inhibiting both cleavage and polyadenylation

Previous studies have demonstrated that Ara-ATP can inhibit poly(A) polymerase activity by competing with ATP. To elucidate the mechanism of action of this compound, its effect on the cleavage and polyadenylation of two specific substrates, SV40L and adenovirus L3 pre-mRNAs, was studied in HeLa nuclear extracts. Unlike cordycepin 5' triphosphate, Ara-ATP inhibited both cleavage and poly(A) addition. Addition of poly(A) polymerase fraction devoid of any other factors required for the processing reactions overcame the inhibitory effect on cleavage as well as polyadenylation of pre-mRNAs. These data suggest that Ara-ATP inhibits both cleavage and polyadenylation reactions by interacting with the ATP-binding site on poly(A) polymerase, the activity of which is essential for the cleavage reaction. Ara-ATP also blocked formation of the post-cleavage and polyadenylation-specific complexes, which further confirmed the inhibitory effect of the ATP analog on the two tightly coupled 3'-end processing reactions.

Intracellular Mg2+ and magnesium depletion in isolated renal thick ascending limb cells

Magnesium reabsorption and regulation within the kidney occur principally within the cortical thick ascending limb (cTAL) cells of the loop of Henle. Fluorometry with the dye, mag-fura-2, was used to characterize intracellular Mg2+ concentration ([Mg2+]i) in single cTAL cells. Primary cell cultures were prepared from porcine kidneys using a double antibody technique (goat anti-human Tamm-Horsfall and rabbit anti-goat IgG antibodies). Basal [Mg2+]i was 0.52 +/- 0.02 mM, which was approximately 2% of the total cellular Mg. Cells cultured (16 h) in high magnesium media (5 mM) maintained basal [Mg2+]i, 0.48 +/- 0.02, in the normal range. However, cells cultured in nominally magnesium-free media possessed [Mg2+]i, 0.27 +/- 0.01 mM, which was associated with a significant increase in net Mg transport, (control, 0.19 +/- 0.03 and low Mg, 0.35 +/- 0.01 nmol.mg-1 protein.min-1) as assessed by 28Mg uptake. Mg(2+)-depleted cells were subsequently placed in high Mg solution (5 mM) and the Mg2+ refill rate was assessed by fluorescence. [Mg2+]i returned to normal basal levels, 0.53 +/- 0.03 mM, with a refill rate of 257 +/- 37 nM/s. Mg2+ entry was not changed by 5.0 mM Ca2+ or 2 mM Sr2+, Cd2+, Co2+, nor Ba2+ but was inhibited by Mn2+ approximately La3+ approximately Gd3+ approximately Zn2+ approximately Be2+ at 2 mM. Intracellular Ca2+ and 45Ca uptake was not altered by Mg depletion or Mg2+ refill, indicating that the entry is relatively specific to Mg2+. Mg2+ uptake was inhibited by nifedipine (117 +/- 20 nM/s), verapamil (165 +/- 34 nM/s), and diltiazem (194 +/- 19 nM/s) but enhanced by the dihydropyridine analogue, Bay K 8644 (366 +/- 71 nM/s). These antagonists and agonists were reversible with removal and [Mg2+]i subsequently returned to normal basal levels. Mg2+ entry rate was concentration and voltage dependent and maximally stimulated after 4 h in magnesium-free media. Cellular magnesium depletion results in increases in a Mg2+ refill rate which is dependent, in part, on de novo protein synthesis. These data provide evidence for novel Mg2+ entry pathways in cTAL cells which are specific for Mg2+ and highly regulated. These entry pathways are likely involved with renal Mg2+ homeostasis.

Cordycepin rapidly collapses the intermediate filament networks into juxtanuclear caps in fibroblasts and epidermal cells

The nucleoside analog 3'-deoxyadenosine (cordycepin) rapidly collapses the intermediate filaments into juxtanuclear caps in interphase fibroblasts and keratinocytes. A minimum of 80 micrograms/ml cordycepin or 20 micrograms/ml cordycepin in combination with 2 micrograms/ml of the deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenosine (EHNA) to inhibit its degradation is required to see these effects. This is the same concentration required for cordycepin to arrest cells at the onset of mitosis and depolymerize the microtubules to small asters. Cordycepin enters the cells rapidly and is phosphorylated to 3'-dATP with a concomitant drop in ATP levels. However, the direct reduction of ATP levels does not mimic the same rapid effects of cordycepin on either the intermediate filaments or microtubules. In addition, similar effects are not produced by a variety of other adenosine analogs with alterations in the 2'- and 3'-ribose positions. Although other pharmacological reagents result in alterations of the fibroblastic intermediate filaments, cordycepin is unusual because of the rapidity with which the fibroblastic intermediate filaments collapse into the juxtanuclear caps. The juxtanuclear caps have a morphology different from that of the perinuclear bundles of intermediate filaments that arise after long-term depolymerization of the microtubules. The keratin fibers in the epidermal cells retract to a perinuclear ring when treated with cordycepin.

Heat-sensitive mutant strain of Neurospora crassa, 4M(t), conditionally defective in 25S ribosomal ribonucleic acid production

A heat-sensitive mutant strain of Neurospora crassa, 4M(t), was studied in an attempt to define its molecular lesion. The mutant strain is inhibited in conidial germination and mycelial extension at the nonpermissive temperature (37 degrees C). Macromolecular synthesis studies showed that both ribonucleic acid (RNA) and protein syntheses are inhibited when 4-h cultures are shifted from 20 to 37 degrees C. Density gradient analysis of ribosomal subunits made at 37 degrees C indicated that strain 4M(t) is deficient in the accumulation of 60S ribosomal subunits in that the ratio of 60S/37S subunits was 0.29:1 compared with 1.6:1 for the parental strain. This phenotype was shown to be the result of a slow rate of processing of, and a deficiency in the amount of, the immediate precursor to 25S ribosomal RNA (the large RNA of the 60S subunit) in the sequence of events constituting the production of mature ribosomal RNAs from the primary transcript of the ribosomal deoxyribonucleic acid, the precursor ribosomal RNA molecule. Analysis of polysomes suggested that the heat-sensitive gene product might function in both the assembly and the function of the 60S ribosomal subunit, since there was a smaller proportion of newly made 60S subunits synthesized at 37 degrees C in the polysome region of the gradients than in the monosome-plus-subunit region. The ribosomal RNA processing defect is apparently responsible for the observed defects in germination and macromolecular synthesis at 37 degrees C, but the precise molecular lesion is not known. On the basis of these results, the heat-sensitive mutant allele in the 4M(t) strain is considered to define the rip1 (ribosome production) gene locus.

RNA synthesis inhibitors on young rat adrenal in primary culture. An ultrastructural study

Adrenal cells of newborn rat adrenals in primary tissue culture were treated with actinomycin D (2, 10 and 25 micrograms/ml), alpha-amanitin (5 and 50 micrograms/ml) and cordycepin (100 micrograms/ml) and studied with the electron microscope. The most striking changes observed with the three drugs were localized on the nucleoli, and consisted, respectively, of segregation (actinomycin D), fragmentation (alpha-amanitin) and microsegregation (cordycepin). These results are consistent with the molecular sites of action of the drugs and are comparable to previous in vivo findings.

Poly-A+ mRNA and defeminization of sexual behavior and gonadotropin secretion in rats

To test the hypothesis that testosterone (T) sexually differentiates gonadotropin secretion and sexual behavior by inducing synthesis of messenger RNA (mRNA), newborn female rats received intrahypothalamic infusions of saline or cordycepin, an adenosine analogue that preferentially inhibits synthesis of polyadenylated mRNA, an hour before they received T propionate (TP) systemically. As adults, controls were anovulatory and did not become sexually receptive when given estradiol benzoate (EB) and progesterone (P). Cordycepin-treated females obtained lordosis quotients (LQs) three times those of controls and most of them ovulated. Cordycepin also curtailed the defeminizing effects of some doses of moxestrol, an artificial estrogen; thus it does not simply block aromatization. Some groups were retested for lordosis using EB and methysergide to bypass P receptors. Methysergide increased LQs in one group that received moxestrol + cordycepin as neonates and that was moderately responsive to P, but it did not increase sexual receptivity among the saline-treated controls. These data suggest that defeminization of sexual behaviour involves more than defeminization of P receptor synthesis.

Cordycepin disrupts the microtubule networks and arrests Nil 8 hamster fibroblasts at the onset of mitosis

The nucleoside analogue 3'-deoxyadenosine (cordycepin) arrests dividing cells at the onset of mitosis in prometaphase. The microtubules in the arrested prometaphase cells depolymerize to two small asters. A minimum of 80 micrograms/ml cordycepin or 20 micrograms/ml cordycepin in combination with 2 micrograms/ml of the deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenosine (EHNA) to inhibit its degradation is required to see these effects. Analysis of cell extracts by high-pressure liquid chromatography indicates that cordycepin enters the cells rapidly and is phosphorylated to 3'-dATP. The intracellular concentration rises almost linearly from 0.7 mM after 15 min to 7 mM by 210 min. Concomitantly the ATP concentration shows a rapid drop from the 4 mM present in controls. However, the direct reduction of ATP levels does not mimic the same rapid effects of cordycepin on the microtubules. In addition, similar effects are not produced by a variety of other adenosine analogues with alterations in the 2' and 3' ribose positions. Although other pharmacological reagents arrest cells at the onset of mitosis, cordycepin is unusual because of the collapse of the microtubule networks to two small asters that radiate from the microtubule-organizing center. 3'-dATP can replace the requirement for ATP or GTP in the vitro polymerization of microtubules from microtubule protein: however, at limiting concentrations of nucleotide it requires approximately two times the concentration of 3'-dATP as ATP to support an equivalent level of microtubule polymerization. This suggests that the effects of cordycepin in vivo may be the result of the depletion of cellular ATP pools and the altered ability of 3'dATP to substitute for ATP-dependent reactions. Current experiments are testing this hypothesis.

Estrogen induction of sexual behavior in female rats and synthesis of polyadenylated messenger RNA in the ventromedial nucleus of the hypothalamus

To test the hypothesis that estrogen stimulates sexual behavior by inducing transcription of polyadenylated messenger RNA, we studied the effects of cordycepin, an adenosine analog that disrupts polyadenylation, on the lordotic responses of ovariectomized female rats made sexually receptive with systemic injections of estradiol benzoate (EB) and progesterone (P). Cordycepin inhibited lordosis when infused into the ventromedial nucleus of the hypothalamus within an hour before the females received EB; its effectiveness varied linearly with dose. It did not significantly alter sexual behavior when infused into the medial preoptic area. A dose of cordycepin that decreased lordosis when infused 1 h before injection of 0.5 microgram EB did not affect the behavior when infused 1 h before injection of 500 micrograms P. Cordycepin does not suppress behavior by blocking estrogen uptake since it did not alter estrogen accumulation by hypothalamic cell nuclei. Cordycepin inhibits ribosomal RNA (rRNA) synthesis as well as polyadenylation. While this probably contributes to cordycepin's inhibitory effects on lordosis, it cannot fully account for them since a cytidine analog that inhibits rRNA synthesis without inhibiting polyadenylation did not mimic cordycepin's behavioral effects. Cordycepin may suppress synthesis of P receptors; however, this could not fully account for its behavioral effects since cordycepin also inhibited lordosis when the P receptor was bypassed by substituting methysergide for P. As assessed by protein synthesis autoradiography, cordycepin's effects are highly localized. The data support the notion that estrogen facilitates female sexual behavior by altering gene expression in the brain.

The effect of biotin on cellular functions in HeLa cells

HeLa cells cultured in a biotin-deficient medium show reduced rate of protein synthesis, DNA synthesis and growth. Addition of exogenous biotin to the cells cultured in biotin-deficient medium results in enhanced protein synthesis, DNA synthesis and cell growth. Continuous protein synthesis is required for the increase in DNA synthesis observed upon the addition of exogenous biotin to the cells cultured in biotin-deficient medium. These results suggest that cells cultured in biotin-deficient medium are arrested in the G1 stage of cell cycle and this block is removed upon the addition of biotin to the deficient medium.

Pterins and the regulation of lymphocyte activation on the mode of xanthopterin action

Some intermediates of pterin anabolism amplify the lectin-induced lymphocyte stimulation while the catabolites xanthopterin and isoxanthopterin terminate their proliferation (Ziegler, I. et al., Cancer Res. 43, 5356 (1983). In the present investigation, we analysed the effect of xanthopterin on total RNA synthesis and on DNA synthesis in both concanavalin A-stimulated lymphocytes and in the lymphoblastoid cell line L 1210. The time courses at various inhibitor concentrations indicated that xanthopterin inhibits RNA synthesis prior to DNA synthesis. Further analysis of the RNA species was performed by double-labeling and subsequent polyacrylamide-gel electrophoresis. Pulse and pulse-chase experiments revealed that an inhibition of 45 S pre-RNA is closer to the target of xanthopterin inhibition than is DNA synthesis.

Endocrine regulation of spermatogenesis in Nereis diversicolor (annelida polychaeta): experimental study of the control of meiotic differentiation

In Nereidae, spermatogenesis is regulated by a hormone secreted by the supraesophageal ganglion (brain hormone). The hormonal concentration decreases with worm age. Spermatogonial proliferation in young worms proceeds under a high hormonal level whereas differentiation of spermatozoa in aged worms occurs in the absence of brain hormone. Spermatogonia were removed from the endocrine influence of the brain in vitro by the organ culture method. Isolated parapodia produced spermatozoa after 13 days. Control cultures were obtained by associating a parapodium with the prostomium of a young worm. It seems that the brain hormone inhibits the spermatocyte differentiation since removal of the brain results in increased RNA synthesis, followed by DNA replication, meiosis, and spermiogenesis (Bertout, '83). Modalities of the hormonal control of meiosis, especially at the level of the RNA syntheses related to meiotic differentiation, were investigated. Effects of reintroducing the hormonal influence during meiotic differentiation were studied through parapodium-prostomium associations at various time after the brain inhibition has been lifted. Effects or RNA inhibitors (actinomycin D, alpha-amanitin, cordycepin) were also tested. The results lead us to propose a hypothesis according to which brain hormone would interfere with molecular events related to the transition from the stage of spermatogonial proliferation (mitotic behavior) to the stage of meiotic differentiation (meiotic behavior).

Newly formed mRNA lacking polyadenylic acid enters the cytoplasm and the polyribosomes but has a shorter half-life in the absence of polyadenylic acid

Labeled adenovirus type 2 nuclear RNA molecules from cells treated with 3'-deoxyadenosine (3'dA) were earlier reported to lack polyadenylic acid [poly(A)], but to be correctly spliced in the nucleus (M. Zeevi et al., Cell 26:39-46, 1981). We have now found that the shortened mRNA molecules, lacking poly(A), can also be found in the cytoplasm of 3'dA-treated cells in association with the polyribosomes. In addition, the accumulation of labeled, nuclear adenovirus-specific RNA complementary to early regions 1a, 1b, and 2 of the adenovirus genome was approximately equal in 3'dA-treated and control cells. At the initial appearance of newly labeled adenovirus type 2 RNA (10 min) in the cytoplasm, there was one-half as much labeled RNA in 3'dA-treated cells as in the control. However, control cells accumulated additional mRNA in the cytoplasm very rapidly in the first 40 min of labeling, whereas the 3'dA-treated cells did not. Therefore, it appears that the correctly spliced, poly(A)- mRNA molecules that are labeled in the presence of 3'dA can be transported from the nucleus with nearly the same frequency and the same exit time as in control cells and can be translated in the cytoplasm but have a much shorter half-life than the poly(A)+ mRNA molecules from control infected cells. From these results it is suggested that the role of poly(A) may be entirely to increase the longevity of cytoplasmic mRNA.

Current concepts: III. Molecular aspects of dietary modulation of transcription and enhanced longevity

Dietary restriction is a known means of prolonging the life span of animals. How diet can increase longevity at the molecular level is not yet known. As organisms age, there is a decrease in the ability ot synthesize RNA and a decrease in protein synthesis indicating that there is an overall loss in gene expression. In addition, a decrease in protein turnover is evident indicating a lack of cellular renewal because of the accumulation of tissue protein. Evidence is presented in this review, that certain dietary regimens appear to be capable of enhancing the synthesis of mRNA and probably also produce enhanced turnover of tissue proteins. It is proposed that the physiological "stress" produced by restricted feeding paradigms can enhance gene expression and that this may be a significant factor in the maintenance of cellular homeostasis for a longer period of time.

Newly formed mRNA lacking polyadenylic acid enters the cytoplasm and the polyribosomes but has a shorter half-life in the absence of polyadenylic acid

Labeled adenovirus type 2 nuclear RNA molecules from cells treated with 3'-deoxyadenosine (3'dA) were earlier reported to lack polyadenylic acid [poly(A)], but to be correctly spliced in the nucleus (M. Zeevi et al., Cell 26:39-46, 1981). We have now found that the shortened mRNA molecules, lacking poly(A), can also be found in the cytoplasm of 3'dA-treated cells in association with the polyribosomes. In addition, the accumulation of labeled, nuclear adenovirus-specific RNA complementary to early regions 1a, 1b, and 2 of the adenovirus genome was approximately equal in 3'dA-treated and control cells. At the initial appearance of newly labeled adenovirus type 2 RNA (10 min) in the cytoplasm, there was one-half as much labeled RNA in 3'dA-treated cells as in the control. However, control cells accumulated additional mRNA in the cytoplasm very rapidly in the first 40 min of labeling, whereas the 3'dA-treated cells did not. Therefore, it appears that the correctly spliced, poly(A)- mRNA molecules that are labeled in the presence of 3'dA can be transported from the nucleus with nearly the same frequency and the same exit time as in control cells and can be translated in the cytoplasm but have a much shorter half-life than the poly(A)+ mRNA molecules from control infected cells. From these results it is suggested that the role of poly(A) may be entirely to increase the longevity of cytoplasmic mRNA.

Nuclear RNA is spliced in the absence of poly(A) addition

Splicing of newly formed nuclear RNA transcripts has been demonstrated during adenovirus type 2 (Ad2) mRNA formation in HeLa cells in the presence of "cordycepin," 3' deoxyadenosine, a drug that stops poly(A) addition to nuclear RNA. Nuclear RNA prepared from Ad2-infected cells after a 30 min label time in the presence or absence of 3' deoxyadenosine was hybridized to and eluted from Ad2 DNA sequences in the transcription units of region E1b and region E2. The nuclear RNA from the 3' dA-treated cells did not contain poly(A) but did contain Ad2-specific molecules approximately 200 to 250 bases shorter than the spliced mRNAs of the control infected cells. In addition, the approximately 2 kb RNA from Ad2 region E2 was shown to have sequences that lie more than 3.5 kb apart on the DNA, suggesting that correct cutting and splicing of the primary transcript in the absence of poly(A) synthesis had occurred. Therefore, although poly(A) addition usually precedes splicing during mRNA formation, poly(A) is not required for splicing.

Heat-sensitive mutant strain of Neurospora crassa, 4M(t), conditionally defective in 25S ribosomal ribonucleic acid production

A heat-sensitive mutant strain of Neurospora crassa, 4M(t), was studied in an attempt to define its molecular lesion. The mutant strain is inhibited in conidial germination and mycelial extension at the nonpermissive temperature (37 degrees C). Macromolecular synthesis studies showed that both ribonucleic acid (RNA) and protein syntheses are inhibited when 4-h cultures are shifted from 20 to 37 degrees C. Density gradient analysis of ribosomal subunits made at 37 degrees C indicated that strain 4M(t) is deficient in the accumulation of 60S ribosomal subunits in that the ratio of 60S/37S subunits was 0.29:1 compared with 1.6:1 for the parental strain. This phenotype was shown to be the result of a slow rate of processing of, and a deficiency in the amount of, the immediate precursor to 25S ribosomal RNA (the large RNA of the 60S subunit) in the sequence of events constituting the production of mature ribosomal RNAs from the primary transcript of the ribosomal deoxyribonucleic acid, the precursor ribosomal RNA molecule. Analysis of polysomes suggested that the heat-sensitive gene product might function in both the assembly and the function of the 60S ribosomal subunit, since there was a smaller proportion of newly made 60S subunits synthesized at 37 degrees C in the polysome region of the gradients than in the monosome-plus-subunit region. The ribosomal RNA processing defect is apparently responsible for the observed defects in germination and macromolecular synthesis at 37 degrees C, but the precise molecular lesion is not known. On the basis of these results, the heat-sensitive mutant allele in the 4M(t) strain is considered to define the rip1 (ribosome production) gene locus.