Classes Of Ribonucleic Acid Research Articles

The role of long non-coding RNAs in carbohydrate and fat metabolism in the liver.

The metabolism of carbohydrates and lipids (fat) in the liver is closely interconnected both in physiological conditions and in pathology. This relationship in the body is possible due to the regulation by many factors, including epigenetic ones. Histone modifications, DNA methylation, and non-coding RNAs are considered to be the main epigenetic factors. Non-coding RNAs (ncRNAs) refers to ribonucleic acid (RNA) molecules that do not code for a protein. They cover a huge number of RNA classes and perform a wide range of biological functions such as regulating gene expression, protecting the genome from exogenous DNA, and directing DNA synthesis. One such class of ncRNAs that has been extensively studied are long non-coding RNAs (lncRNAs). The important role of lncRNAs in the formation and maintenance of normal homeostasis of biological systems, as well as participation in many pathological processes, has been proven. The results of recent studies indicate the importance of lncRNAs in lipid and carbohydrate metabolism. Modifications of lncRNAs expression can lead to disruption of biological processes in tissues, including fat and protein, such as adipocyte proliferation and differentiation, inflammation, and insulin resistance. Further study of lncRNAs made it possible to partly determine the regulatory mechanisms underlying the formation of an imbalance in carbohydrate and fat metabolism individually and in their relationship, and the degree of interaction between different types of cells involved in this process. This review will focus on the function of lncRNAs and its relation to hepatic carbohydrate and fat metabolism and related diseases in order to elucidate the underlying mechanisms and prospects for studies with lncRNAs.

EL-RMLocNet: An explainable LSTM network for RNA-associated multi-compartment localization prediction

Subcellular localization of Ribonucleic Acid (RNA) molecules provide significant insights into the functionality of RNAs and helps to explore their association with various diseases. Predominantly developed single-compartment localization predictors (SCLPs) lack to demystify RNA association with diverse biochemical and pathological processes mainly happen through RNA co-localization in multiple compartments. Limited multi-compartment localization predictors (MCLPs) manage to produce decent performance only for target RNA class of particular sub-type. Further, existing computational approaches have limited practical significance and potential to optimize therapeutics due to the poor degree of model explainability. The paper in hand presents an explainable Long Short-Term Memory (LSTM) network “EL-RMLocNet”, predictive performance and interpretability of which are optimized using a novel GeneticSeq2Vec statistical representation learning scheme and attention mechanism for accurate multi-compartment localization prediction of different RNAs solely using raw RNA sequences. GeneticSeq2Vec generates optimized statistical vectors of raw RNA sequences by capturing short and long range relations of nucleotide k-mers. Using sequence vectors generated by GeneticSeq2Vec scheme, Long Short Term Memory layers extract most informative features, weighting of which on the basis of discriminative potential for accurate multi-compartment localization prediction is performed using attention layer. Through reverse engineering, weights of statistical feature space are mapped to nucleotide k-mers patterns to make multi-compartment localization prediction decision making transparent and explainable for different RNA classes and species. Empirical evaluation indicates that EL-RMLocNet outperforms state-of-the-art predictor for subcellular localization prediction of 4 different RNA classes by an average accuracy figure of 8% for Homo Sapiens species and 6% for Mus Musculus species. EL-RMLocNet is freely available as a web server at (https://sds_genetic_analysis.opendfki.de/subcellular_loc/).

Non-Coding RNAs and Hereditary Hemorrhagic Telangiectasia.

Non-coding RNAs (ncRNAs) are functional ribonucleic acid (RNA) species that include microRNAs (miRs), a class of short non-coding RNAs (∼21–25 nucleotides), and long non-coding RNAs (lncRNAs) consisting of more than 200 nucleotides. They regulate gene expression post-transcriptionally and are involved in a wide range of pathophysiological processes. Hereditary hemorrhagic telangiectasia (HHT) is a rare disorder inherited in an autosomal dominant fashion characterized by vascular dysplasia. Patients can develop life-threatening vascular malformations and experience severe hemorrhaging. Effective pharmacological therapies are limited. The study of ncRNAs in HHT is an emerging field with great promise. This review will explore the current literature on the involvement of ncRNAs in HHT as diagnostic and pathogenic factors.

RNA modifications and the link to human disease.

Ribonucleic acid (RNA) is involved in translation and transcription, which are the mechanisms in which cells express genes (Alberts et al., 2002). The three classes of RNA discussed are transfer RNA (tRNA), messenger RNA (mRNA), and ribosomal RNA (rRNA). mRNA is the transcript encoded from DNA, rRNA is associated with ribosomes, and tRNA is associated with amino acids and is used to read mRNA transcripts to make proteins (Lodish, Berk, Zipursky, et al., 2000). Interestingly, the function of tRNA, rRNA, and mRNA can be significantly altered by chemical modifications at the co-transcriptional and post-transcriptional levels, and there are over 171 of these modifications identified thus far (Boccaletto et al., 2018; Modomics-Modified bases, 2017). Several of these modifications are linked to diseases such as cancer, diabetes, and neurological disorders. In this review, we will introduce a few RNA modifications with biological functions and how dysregulation of these RNA modifications is linked to human disease.

Characterization of the Catalytic Subunits of the RNA Exosome-like Complex in Plasmodium falciparum.

The eukaryotic ribonucleic acid (RNA) exosome is a versatile multiribonuclease complex that mediates the processing, surveillance, and degradation of virtually all classes of RNA in both the nucleus and cytoplasm. The complex, composed of 10 to 11 subunits, has been widely described in many organisms. Bioinformatic analyses revealed that there may be also an exosome‐like complex in Plasmodium falciparum, a parasite of great importance in public health, with eight predicted subunits having high sequence similarity to their counterparts in yeast and human. In this work, the putative RNA catalytic components, designated as PfRrp4, PfRrp41, PfDis3, and PfRrp6, were identified and systematically analyzed. Quantitative polymerase chain reaction (QPCR) analyses suggested that all of them were transcribed steadily throughout the asexual stage. The expression of these proteins was determined by Western blot, and their localization narrowed to the cytoplasm of the parasite by indirect immunofluorescence. The recombinant proteins of PfRrp41, PfDis3, and PfRrp6 exhibited catalytic activity for single‐stranded RNA (ssRNA), whereas PfRrp4 showed no processing activity of both ssRNA and dsRNA. The identification of these putative components of the RNA exosome complex opens up new perspectives for a deep understanding of RNA metabolism in the malarial parasite P. falciparum.

Shining a Brighter Light on Genomic Dark Material

“Perhaps the biggest surprise of the post-genomic era has been the enormous number and diversity of transcriptional products arising from the previously presumed wastelands of the non-protein-coding genome,” write John Mattick and John Rinn of the Garvan Institute of Medical Research and Harvard University, respectively, in the January 2015 issue of Nature Structural and Molecular Biology. “In fact,” David Spector of the Cold Spring Harbor Laboratory points out, “70 to 80 percent of the human genome is likely to be transcribed, yielding a complex network of overlapping transcripts that includes tens of thousands of long ribonucleic acids (RNAs) with little or no protein-coding capacity.” Many long non-protein-coding RNAs (lncRNAs) are proving to be key regulators of gene expression, whereas others act as molecular decoys, serve as small RNA precursors, act as scaffolds for protein–protein interactions, or drive nuclear organization. In addition, “emerging evidence suggests that a number of lncRNAs help guide epigenetic complexes to their sites of action, control chromatin architecture, and participate in embryo development,” says Mattick. To complicate matters even further, some lncRNAs do have, in addition to their primary talents, the ability to encode proteins—albeit usually only small ones. Ron Breaker and his colleagues at Yale are making significant progress identifying the roles of several giant, very complicated noncoding RNAs discovered in extremophilic bacteria, whose mysterious functions sometimes help the cells cope with unusual environmental stresses. An ornate, large extremophilic (OLE) RNA recently identified in Bacillus halodurans, for example, seems to protect its host bacterium against both alcohol-induced stress and cold. However, two other newly discovered structures—GOLLD (giant, ornate, lakeand lactobacillales-derived) and HEARO (HNH endonucleaseassociated RNA and open reading frame)—so far appear to do bacteria more harm than good. Notably though, both GOLLD and HEARO have the distinction of being among the most complex, giant RNAs ever encountered. GOLLD is “particularly striking because it’s the third biggest highly structured bacteria-associated RNA ever described, ranking only behind 23S and 16S ribosomal RNAs,” according to the Breaker Lab’s Zasha Weinberg. But GOLLD sits on a prophage, probably helping it to survive, mature into an adult virus, and infect; therefore, it is no friend to bacteria. Similarly, HEARO looks and acts like a mobile genetic element and replicates promiscuously in its target bacteria, which could do some harm, at least in the short term. Eventually, however, the challenge to its hosts might drive evolution, which could make HEAROinfected bacteria better able to deal with their environments. (The benefits of genetic conflict are detailed in “Rules of conduct: Ancient battles between viruses and hosts,” in the June 2014 issue of BioScience (http://io.aibs. org/virhost). In contrast to bacterial lncRNAs, the functions of most lncRNAs so far identified in multicellular organisms are still unknown. However, many more of these intriguing regulatory RNAs in both simple and complex organisms await discovery, say the experts. Therefore, identifying new lncRNAs and figuring out what they do has grown into a robust scientific industry, keeping hundreds or maybe even thousands of researchers around the world busy. The recent explosion of new technologies is expected to make their jobs easier. Long noncoding RNAs, for example, can now be identified with high-throughput sequencing instead of optical imaging, says Stanford University’s Howard Y. Chang, who considers this is a major advance. “Likewise, traditional in vitro purification methods are being replaced by [more accurate] in vivo testing,” adds Ci Chu, also at Stanford. Furthermore, low-throughput RNA-mapping has been combined with next-generation sequencing, and that helps provide a wider range of information. Notably, lncRNA itself is a vague catch-all grouping into which any transcript that doesn’t appear to have protein coding as its primary job and is larger than 200 nucleotides in length qualifies for inclusion. “The size is arbitrary but has the advantage of being a convenient biophysical cutoff that excludes most known, albeit also poorly understood, classes of small regulatory and other RNAs. However, even messenger RNAs sometimes moonlight as functional lncRNA,” Chang says. But even though alternative terminology has been suggested, for the time being, RNAists have settled comfortably (or not) on lncRNA. “As confusing as it might sometimes be, the complexity and interconnectedness of lncRNAs should not be an impediment to but rather the motivation for exploring the vast unknown universe of RNA regulation, without which we will not understand biology,” argues Mattick.

Enhanced detection of post-transcriptional modifications using a mass-exclusion list strategy for RNA modification mapping by LC-MS/MS.

There has been a renewed appreciation for the dynamic nature of ribonucleic acid (RNA) modifications and for the impact of modified RNAs on organism health resulting in an increased emphasis on developing analytical methods capable of detecting modifications within specific RNA sequence contexts. Here we demonstrate that a DNA-based exclusion list enhances data dependent liquid chromatography tandem mass spectrometry (LC-MS/MS) detection of post-transcriptionally modified nucleosides within specific RNA sequences. This approach is possible because all post-transcriptional modifications of RNA, except pseudouridine, result in a mass increase in the canonical nucleoside undergoing chemical modification. Thus, DNA-based sequences reflect the state of the RNA prior to or in the absence of modification. The utility of this exclusion list strategy is demonstrated through the RNA modification mapping of total tRNAs from the bacteria Escherichia coli, Lactococcus lactis, and Streptomyces griseus. Creation of a DNA-based exclusion list is shown to consistently enhance the number of detected modified ribonuclease (RNase) digestion products by ∼20%. All modified RNase digestion products that were detected during standard data dependent acquisition (DDA) LC-MS/MS were also detected when the DNA-based exclusion list was used. Consequently, the increase in detected modified RNase digestion products is attributed to new experimental information only obtained when using the exclusion list. This exclusion list strategy should be broadly applicable to any class of RNA and improves the utility of mass spectrometry approaches for discovery-based analyses of RNA modifications, such as are required for studies of the epitranscriptome.

Basic concepts and potential applications of genetics and genomics for cardiovascular and stroke clinicians: a scientific statement from the American Heart Association.

Although genetics and genomics play an increasingly large role in the practice of medicine, the clinical care of patients suffering from cardiovascular disease or stroke has not been significantly affected. This is despite the tremendous strides being made to understand the genetic basis of both rare and common cardiovascular and stroke disorders through techniques such as genome-wide association studies (GWASs) and next-generation sequencing studies. Much of this knowledge remains to be translated to the clinic and must be subjected to clinical trials to ensure patient safety and a meaningful impact on clinical outcomes. However, even if this knowledge were to be successfully implemented into clinical practice, a potential barrier to widespread adoption is a lack of familiarity with basic concepts of genetics and genomics. Another concern is the possibility of the emergence of a significant gap in clinical care provided by practitioners who are informed about the clinical use of genetics and genomics knowledge and those who are not. Thus, there is a critical need to foster genetics/genomics literacy among all involved in the care of cardiovascular and stroke patients because it can be expected that these topics will transform the way medicine is practiced. The purpose of this document is to serve as a resource for practitioners in cardiovascular and stroke medicine on the application of genetics and genomics to patient care. Although not exhaustive, it contains an overview of the field written specifically to be accessible and relevant to practitioners. It also refers to additional educational materials available in the literature, in textbooks, and on the Internet. (Because this article is intended to be primarily educational in nature, rather than providing a review of the literature, citations are limited to a small number of research articles and reviews of exceptional interest.) It recommends a core knowledge base with …

PREDICTION OF SECONDARY STRUCTURE OF RNAs WITH PSEUDOKNOTS USING MATCHED FILTERS

Prediction of ribonucleic acid (RNA) secondary structure is an important task in bioinformatics. The RNA structure is known to influence its biological functionality. RNA secondary structure contains many substructures such as stems, loops and pseudoknots. The substructure pseudoknot occurs in several classes of RNAs, and plays a vital role in many biological processes. Prediction of pseudoknots in RNA is challenging and still an open research problem. Several computational methods based on dynamic programming, genetic algorithms, statistical models, etc., have been proposed with varying success. In this paper, we employ matched filtering approach to determine the RNA secondary structure containing pseudoknots. The central idea is to use a matched filter to identify the longest possible stem patterns in the base-pairing matrix of an RNA. The stem patterns obtained are then used to determine the locations of the other substructures such as loops and pseudoknots present in the RNA. Comparison of the prediction results, for RNA sequences derived from PseudoBase, illustrate the effectiveness and the accuracy of our proposed approach as compared to some of the existing popular RNA secondary structure prediction methods.

Disruption of a Large Intergenic Noncoding RNA in Subjects with Neurodevelopmental Disabilities

Large intergenic noncoding (linc) RNAs represent a newly described class of ribonucleic acid whose importance in human disease remains undefined. We identified a severely developmentally delayed 16-year-old female with karyotype 46,XX,t(2;11)(p25.1;p15.1)dn in the absence of clinically significant copy number variants (CNVs). DNA capture followed by next-generation sequencing of the translocation breakpoints revealed disruption of a single noncoding gene on chromosome 2, LINC00299, whose RNA product is expressed in all tissues measured, but most abundantly in brain. Among a series of additional, unrelated subjects referred for clinical diagnostic testing who showed CNV affecting this locus, we identified four with exon-crossing deletions in association with neurodevelopmental abnormalities. No disruption of the LINC00299 coding sequence was seen in almost 14,000 control subjects. Together, these subjects with disruption of LINC00299 implicate this particular noncoding RNA in brain development and raise the possibility that, as a class, abnormalities of lincRNAs may play a significant role in human developmental disorders.

SARNA-Predict: Accuracy Improvement of RNA Secondary Structure Prediction Using Permutation-Based Simulated Annealing

Ribonucleic acid (RNA), a single-stranded linear molecule, is essential to all biological systems. Different regions of the same RNA strand will fold together via base pair interactions to make intricate secondary and tertiary structures that guide crucial homeostatic processes in living organisms. Since the structure of RNA molecules is the key to their function, algorithms for the prediction of RNA structure are of great value. In this article, we demonstrate the usefulness of SARNA-Predict, an RNA secondary structure prediction algorithm based on Simulated Annealing (SA). A performance evaluation of SARNA-Predict in terms of prediction accuracy is made via comparison with eight state-of-the-art RNA prediction algorithms: mfold, Pseudoknot (pknotsRE), NUPACK, pknotsRG-mfe, Sfold, HotKnots, ILM, and STAR. These algorithms are from three different classes: heuristic, dynamic programming, and statistical sampling techniques. An evaluation for the performance of SARNA-Predict in terms of prediction accuracy was verified with native structures. Experiments on 33 individual known structures from eleven RNA classes (tRNA, viral RNA, antigenomic HDV, telomerase RNA, tmRNA, rRNA, RNaseP, 5S rRNA, Group I intron 23S rRNA, Group I intron 16S rRNA, and 16S rRNA) were performed. The results presented in this paper demonstrate that SARNA-Predict can out-perform other state-of-the-art algorithms in terms of prediction accuracy. Furthermore, there is substantial improvement of prediction accuracy by incorporating a more sophisticated thermodynamic model (efn2).

Ribozymes: biology, biochemistry, and implications for clinical medicine

Ribozymes are a class of ribonucleic acid (RNA) molecules that possess enzymatic properties. Upon binding to complementary nucleic acid strands, catalytic degradation takes place via a cleavage reaction. In effect, inactivation of susceptible substrate RNA molecules takes place at a catalytic rate and with a high degree of substrate specificity. This article reviews the biology and biochemistry of this class of molecules and its potential applications in clinical medicine.

Actin gene expression in developing sea urchin embryos.

We show that the synthesis of actin is regulated developmentally during early sea urchin embryogenesis and that the level of synthesis of this protein parallels the steady-state amounts of the actin messenger ribonucleic acids (RNA). An in vitro translation and RNA blotting analysis of embryo RNA from several stages of early development indicated that during the first 8 h after fertilization there was a low and relatively constant level of actin messenger RNA in the embryo. Between 8 and 13 h of development, the amount of actin messenger RNA began to increase both in the cytoplasm and on polysomes, and by 18 h the amounts of actin message per embryo had risen between approximately 10- and 25-fold in the cytoplasm and between 15- and 40-fold on polysomes. Two size classes of actin messenger RNA (2.2 and 1.8 kilobases) were identified in unfertilized eggs and in all of the developmental stages examined. The amount of each actin message class increased over a similar time interval during early development. However, the amounts of these size classes in the cytoplasm relative to each other shifted between the earliest stages examined (2 to 5 h) and the hatching blastula stage (18 h), with the ratio of the 1.8-kilobase actin messenger RNA to the 2.2-kilobase actin messenger RNA increasing almost threefold during this period.

Actin gene expression in developing sea urchin embryos.

We show that the synthesis of actin is regulated developmentally during early sea urchin embryogenesis and that the level of synthesis of this protein parallels the steady-state amounts of the actin messenger ribonucleic acids (RNA). An in vitro translation and RNA blotting analysis of embryo RNA from several stages of early development indicated that during the first 8 h after fertilization there was a low and relatively constant level of actin messenger RNA in the embryo. Between 8 and 13 h of development, the amount of actin messenger RNA began to increase both in the cytoplasm and on polysomes, and by 18 h the amounts of actin message per embryo had risen between approximately 10- and 25-fold in the cytoplasm and between 15- and 40-fold on polysomes. Two size classes of actin messenger RNA (2.2 and 1.8 kilobases) were identified in unfertilized eggs and in all of the developmental stages examined. The amount of each actin message class increased over a similar time interval during early development. However, the amounts of these size classes in the cytoplasm relative to each other shifted between the earliest stages examined (2 to 5 h) and the hatching blastula stage (18 h), with the ratio of the 1.8-kilobase actin messenger RNA to the 2.2-kilobase actin messenger RNA increasing almost threefold during this period.

Pattern of ribonucleic acid synthesis during germination of Allomyces macrogynus mitospores

The relationship between ribonucleic acid (RNA) synthesis and germination of Allomyces macrogynus mitospores was investigated. It was determined that the synthesis of all classes of RNA was initiated during the first 10 min of germination, around the time of encystment. It is during this stage that the membrane of the nuclear cap structure begins to break down, dispersing the cell complement of ribosomes throughout the cytoplasm. After encystment, there was an increase in the rate of synthesis of the four stable RNA species (4S, 5S, 19S, and 27S) which leveled off as the germ tube emerged. Data suggested that messenger RNA was synthesized at an increasing rate during the course of germination. Studies of RNA precursor pool behavior and RNA synthesis in the presence and absence of actinomycin D indicated that no species of RNA, including messenger RNA, was synthesized in the presence of actinomycin D. Further, precursor pool measurement indicated that the apparent increase in the rate of RNA synthesis during germination was largely due to increased specific activity of the RNA precursor pool.

New class of ribonucleic acid in Neurospora associated with the outer cell envelope.

Extrinsic ribonucleic acid (RNA) can be isolated from a KCl extract of Neurospora crassa conidial cell surface products. It is heterogeneous in size. The bulk of this RNA travels as a broad band, trailing the 5.8S ribosomal marker RNA on electrophoretic gels. The extrinsic RNA, when denatured, exhibites several discrete lengths between 50,000 and 130,000 daltons. Melting profiles confirm the heterogeneity of the RNA and indicate that 58% of the bases are involved in hydrogen bonding. Analyses of alkaline hydrolysis products reveal no extensive methylation and few or none of the unusual bases present in transfer RNA. The bases are present in approximately equivalent amounts. Extrinsic RNA represents 2 to 3% of the total cellular RNA. Since this membrane-associated class of RNA does not resemble ribosomal RNA, messenger RNA, or transfer RNA and since it is extracted from the cell exterior by methods used to remove extrinsic membrane molecules, we have designated it extrinsic RNA.

Poly(uridylic acid) sequences in messenger ribonucleic acid of HeLa cells

The poly(uridylic acid [poly(U)] sequences of 30 to 40 nucleotides found in the heterogeneous nuclear ribonucleic acid (RNA) Of HeLa cells are also present in the poly(adenylic acid) [poly(A)] containing messenger RNA (mRNA) of these cells. Twenty-five percent of the total poly(U) sequences in the cell are found in the cytoplasm after HeLa cells have been labeled for 2.5 h with 32P. This value is close to 40% if only poly(A) containing RNA molecules of the cell are considered. The distribution of poly(U) sequences parallels that of poly(A) sequences in different size classes of cytoplasmic messenger RNA. From the concentrations and lengths of the two sequences it can be estimated that about 20% of the poly(A) containing mRNA molecules could contain one poly(U) sequence. Several lines of evidence have been developed to rule out poly(U) containing heterogeneous nuclear RNA (HnRNA) as the source of the poly(U) sequences in cytoplasm. Poly(U) sequences are also found in RNA molecules of the nucleus and cytoplasm which do not contain poly(A). Although poly(U) sequences are most abundant in nuclear RNA species lacking poly(A), they are well represented in a class of RNA molecules in cytoplasm which lack poly(A), but which otherwise resemble the polysomal mRNA of HeLa cells.

Macromolecule synthesis in a mutant of Saccharomyces cerevisiae inhibited by S-adenosyimethionine.

Saccharomyces cerevisiae strain 83384-B3 carries the sai-1 mutation which confers sensitivity to S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). It was shown that the mutant is impermeable to precursors of ribonucleic acid (RNA) and protein during inhibition by SAM (0.2 mM). Inhibition of uptake of adenine and uracil was nearly complete 3 h after growth in the presence of SAM and the uptake of leucine was at least 10-fold lower. The incorporation of 3H-adenine into ribosomal RNA, transfer RNA and heterodisperse RNA, believed to be messenger, was reduced 10-fold when measured after 1 h inhibition. The inhibition of growth was completely reversed by methionine (2.0 mM) in cells previously exposed to SAM for 90 min. The polysome content in cells inhibited by SAM was 25% less than the control after 4 h inhibition. Ribosome synthesis increased only about 40% in the presence of SAM and about 5-fold in the control over an 8 h period. All classes of RNA were synthesized during inhibition.

Rifampin: Inhibition of Ribonucleic Acid Synthesis After Potentiation by Amphotericin B in Saccharomyces cerevisiae

The inhibition of Saccharomyces cerevisiae growth by amphotericin B and rifampin was studied. Rifampin alone had no effect on growth or macromolecular syntheses. Lethal amounts of amphotericin B produced a late inhibition of ribonucleic acid (RNA) synthesis simultaneous with the arrest of growth and protein synthesis. In contrast, low doses of amphotericin B along with rifampin caused an early arrest of RNA synthesis, followed by a later arrest of growth and protein synthesis. Used with rifampin, amphotericin B thus appears to increase cell permeability for rifampin, which in turn inhibits RNA synthesis; such results are consistent with some reports of inhibition of yeast RNA polymerase function by rifampin. Experiments with petite mutants ruled out any special effect of the antibiotics on mitochondrial RNA synthesis, so that nuclear RNA synthesis is affected. Acrylamide gel analyses of RNA pulse-labeled after addition of the two antibiotics in synergy showed that synthesis of all major classes of RNA was progressively and uniformly inhibited.

Viruslike particles associated with an isolate of Penicillium brevi-compactum

Viruslike particles (VLPs) found in an isolate of P. brevi-compactum Dierckx were purified by chloroform clarification, differential and density-gradient centrifugation followed by density-gradient electrophoresis. The particles were spherical and measured 40 nm in diameter. The preparations contained a minor and major component with sedimentation rates of 128 and 147 S, respectively. They had a typical nucleoprotein ultraviolet absorption spectrum and contained ribonucleic acid (RNA). The RNA was judged to be double-stranded from its resistance to ribonuclease digestion and hyperchromicity profile. Three size classes of RNA with molecular weights of 2.18, 1.99, and 1.89 × 10 6 daltons were determined by polyacrylamide gel electrophoresis. The P. brevi-compactum isolate was freed of the VLPs by heat treatment which resulted in no change in the growth or morphological characteristics of the culture. Antisera to the VLPs did not react with VLPs from Penicillium stoloniferum Thom, “heat cured” isolates of P. brevi-compactum or other particulate fractions from P. brevi-compactum. The VLPs were considered viral in nature on the basis of their physical properties and the ability of the fungal isolate to be heat cured.