The Effect of Auxin and Abscisic Acid on the Catabolism of RNA

Abscisic acid (ABA) reduced growth in a root test (lentil),but the inhibition observed was less noticeable than that producedby using indol-3yl-acetic acid (IAA) alone. When both ABA andIAA were employed together, ABA acted as a growth-antagonistof IAA. ABA produced a strong inhibition of the total RNA accumulationand accelerated the RNase activity, while IAA strongly stimulatedthe RNA accumulation and greatly inhibited RNase activity. WhenABA and IAA were tested together, ABA also acted as an antagonistof TAA.     

Detection of Avian Tumor Virus RNA in Uninfected Chicken Embryo Cells

Uninfected chicken embryo cells were analyzed for the presence of viral ribonucleic acid (RNA) by molecular hybridization with the single-stranded deoxyribonucleic acid (DNA) product of the RNA-dependent DNA polymerase contained in avian sarcoma-leukosis virions. Viral RNA was detected in all cells which contained the avian tumor virus group-specific antigen and the virus-related helper factor. The amounts of viral RNA in these cells ranged from approximately 3 to 40 copies of viral-specific sequences per cell. In general, the viral RNA content correlated with the level of helper activity in the cells. Cells infected with Rous-associated virus 2 contained 3,000 to 4,000 copies of viral RNA per cell. RNA from these infected cells hybridized with nearly 100% of the viral (3)H-DNA. By contrast, a maximum of less than 50% hybridization was obtained with RNA from the uninfected helper-positive cells, suggesting that not all of the viral RNA sequences were present in these cells. No viral RNA was detected in cells which lacked group-specific antigen and helper activity. Under the conditions used in these studies, less than 0.3 viral genome equivalents of RNA per cell would have been detected.     

RNA-Dependent DNA Polymerase Activity of RNA Tumor Viruses II. Directing Influence of RNA in the Reaction

The role of ribonucleic acid (RNA) in deoxyribonucleic acid (DNA) synthesis with the purified DNA polymerase from the avian myeloblastosis virus has been studied. The polymerase catalyzes the synthesis of DNA in the presence of four deoxynucleoside triphosphates, Mg(2+), and a variety of RNA templates including those isolated from avian myeloblastosis, Rous sarcoma, and Rauscher leukemia viruses; phages f2, MS2, and Qbeta; and synthetic homopolymers such as polyadenylate.polyuridylic acid. The enzyme does not initiate the synthesis of new chains but incorporates deoxynucleotides at 3' hydroxyl ends of primer strands. The product is an RNA.DNA hybrid in which the two polynucleotide components are covalently linked. Free DNA has not been detected among the products formed with the purified enzyme in vitro. The DNA synthesized with avian myeloblastosis virus RNA after alkaline hydrolysis has a sedimentation coefficient of 6 to 7S.     

Mouse DNA replicase. DNA polymerase associated with a novel RNA polymerase activity to synthesize initiator RNA of strict size

De novo DNA synthesis on poly(dT) by a novel mouse DNA polymerase, here named "DNA replicase," was examined for the synthesis of RNA which functions as a primer in the subsequent synthesis of DNA. As has been reported previously (Yagura, T., Kozu, T., and Seno, T. (1982) J. Biochem. (Tokyo) 91, 607-618), a novel RNA polymerase activity, which is distinguished from those of classical RNA polymerases, is associated with DNA replicase. The synthesis of RNA and DNA by DNA replicase (Mr = 16 X 10(4), by glycerol gradient sedimentation analysis) was greatly stimulated by a specific stimulating factor (Mr = 13 X 10(4), by glycerol gradient sedimentation analysis) which was found to consist of two subunits (Mr = 63 X 10(3), by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Nearest neighbor analysis in which transfer of 32P from alpha-labeled nucleoside triphosphates to ribo- and deoxyribonucleotides was examined, showed th at RNA of 8-10 nucleotides long was covalently linked to the 5'-end of the DNA product molecule. This RNA, named initiator RNA, had a triphosphate group at its 5' terminus and its size and synthesis were little affected by the addition of high concentrations of deoxynucleoside triphosphate, while in these conditions deoxyribonucleotides were incorporated into initiator RNA to a limited extent. The characteristics of the DNA replicase and stimulating factor that cooperate to synthesize initiator RNA for subsequent DNA synthesis on single-stranded DNA are important because these components seem to be involved in a reaction required to initiate the synthesis of discontinuous earliest DNA intermediates (Okazaki fragments) in chromosomal DNA replication of eukaryotic cells.     

Modulation of DNA and RNA by PNA

Peptide nucleic acid (PNA), a synthetic DNA mimic that is devoid of the (deoxy)ribose-phosphate backbone yet still perfectly retains the ability to recognize natural nucleic acids in a sequence-specific fashion, can be employed as a tool to modulate gene expressions via several different mechanisms. The unique strength of PNA compared to other oligonucleotide analogs is its ability to bind to nucleic acid targets with secondary structures such as double-stranded and quadruplex DNA as well as RNA. This digest aims to introduce general readers to the advancement in the area of modulation of DNA/RNA functions by PNA, its current status and future research opportunities, with emphasis on recent progress in new targeting modes of structured DNA/RNA by PNA and PNA-mediated gene editing.     

The effects of abscisic Acid on growth and nucleic Acid synthesis in excised embryonic bean axes

Abscisic acid (ABA) is an effective inhibitor of cell elongation in excised embryonic bean axes whether added prior to or after the initiation of cell elongation. Zeatin partially reverses this growth inhibition. ABA inhibits ³²P incorporation into ribosomal RNA, transfer RNA, and DNA but not into the tenaciously bound fraction of elongating axes in a manner resembling 5-fluorouracil, a compound which does not inhibit axis growth. The methylated albumin on kie-selguhr elution profiles of nucleic acids obtained from axes treated with either ABA, 5-fluorouracil, or a combination of the two are similar, and zeatin treatment has little apparent effect on these results. Our results suggest that the inhibition of growth in the axes by ABA is not due to its inhibition of DNA synthesis.     

Retarding effect of inhibitors of protein and RNA synthesis on chlorophyll and protein breakdown

Cycloheximide, ethionine,p-fluorophenylalanine, 6-azauracil, 5-diazouracil and vanillin, applied at relatively high concentrations, retarded the yellowing of kale (Brassica oleracea L. var.acephala) leaf discs in darkness, and stimulated it in light. All the compounds inhibited protein synthesis and retarded protein breakdown. Cycloheximide,p-fluorophenylalanine, diazouracil and vanillin also inhibited the incorporation of uracil-¹⁴C into RNA of senescing discs. Abscisic acid and 2-chloroethylphosphonic acid accelerated yellowing both in darkness and in light and stimulated the protein breakdown in senescing discs. Abscisic acid inhibited the chlorophyll, protein and RNA synthesis in detached, greening cucumber cotyledons. There was no direct correlation between the activity of a given compound as an inhibitor of yellowing in darkness, and the degree of inhibition of RNA synthesis. The arrest of yellowing in darkness is possibly a consequence of the retarded rate of protein breakdown. Yellowing in light, on the contrary, is dependent on the actual rate of protein synthesis.     

Specificity of sigma-dependent binding of RNA polymerase to DNA

Summary Although a large number of E. coli RNA polymerase molecules can bind to phage T3 DNA, not more than three remain bound per DNA template after addition of poly inosinic acid (poly I) which has a high affinity for the enzyme. These stable complexes are able to initiate RNA chains without lag as the enzyme is resistant against rifampicin if substrate is added simultaneously with the drug. Poly I resistant complexes decay very rapidly in the cold (Fig. 2) and are not formed in the absence of the polymerase factor (Table 2). The data provide additional support for the idea that the factor effects the binding of the enzymes to specific sites on the DNA template.     

An RNA ligase from Deinococcus radiodurans

Although DNA repair pathways have been the focus of much attention, there is an emerging appreciation that distinct pathways exist to maintain or manipulate RNA structure in response to breakage events. Here we identify an RNA ligase (DraRnl) from the radiation-resistant bacterium Deinococcus radiodurans. DraRnl seals 3'-OH/5'-PO4 RNA nicks in either a duplex RNA or an RNA: DNA hybrid, but it cannot seal 3'-OH/5'-PO4 DNA nicks. The specificity of DraRnl arises from a requirement for RNA on the 3'-OH side of the nick. DraRnl is a 342-amino acid monomeric protein with a distinctive structure composed of a C-terminal adenylyltransferase domain linked to an N-terminal module that resembles the OB-fold of phenylalanyl-tRNA synthetases. RNA sealing activity was abolished by mutation of the predicted lysine adenylylation site (Lys-165) in the C-terminal domain and was reduced by an order of magnitude by deletion of the N-terminal OB module. Our findings highlight the existence of an RNA repair capacity in bacteria and support the hypothesis that contemporary DNA ligases, RNA ligases, and RNA capping enzymes evolved by the fusion of ancillary effector domains to an ancestral catalytic module involved in RNA repair.