Discontinuous transcription of ribosomal DNA in human cells

Numerous studies show that various genes in all kinds of organisms are transcribed discontinuously, i.e. in short bursts or pulses with periods of inactivity between them. But it remains unclear whether ribosomal DNA (rDNA), represented by multiple copies in every cell, is also expressed in such manner. In this work, we synchronized the pol I activity in the populations of tumour derived as well as normal human cells by cold block and release. Our experiments with 5-fluorouridine (FU) and BrUTP confirmed that the nucleolar transcription can be efficiently and reversibly arrested at +4°C. Then using special software for analysis of the microscopic images, we measured the intensity of transcription signal (incorporated FU) in the nucleoli at different time points after the release. We found that the ribosomal genes in the human cells are transcribed discontinuously with periods ranging from 45 min to 75 min. Our data indicate that the dynamics of rDNA transcription follows the undulating pattern, in which the bursts are alternated by periods of rare transcription events.

Specific detection of RNA on ultra-thin sections

In this paper, we describe a specific method for ultrastructural detection of RNA. Our method is based in the bromination "in situ" of uridine residues in the RNA, which allows the detection of brominated RNA with specific antibodies against bromo-deoxyuridine. With this method we can achieve high specificity and resolution, and it can be applied to Epon or acrylic resin embedded material.

The development of a monoclonal antibody specific for a 2(')-C-allyl modification of uridine, and its use in the localization of ribozymes in vivo

Ribozymes are catalytically active RNA molecules that cleave other RNA molecules in a sequence-specific fashion, with significant turnover. The successful design and synthesis of ribozymes with modifications to increase their stability in biological fluids, while maintaining catalytic activity, has been instrumental in moving this technology from the laboratory into clinical trials. With the entry of ribozymes into the clinical setting, the need has arisen for reagents and/or assays to detect these drugs in tissues. We have developed a monoclonal antibody to the 2(')-deoxy-2(')-C-allyl uridine modification present in our synthetic hammerhead ribozymes. The monoclonal antibody, termed CA1USR, is a murine IgG1(k), whose epitope appears to involve both the 2(')-C-allyl modification, and the uridine base. Use of CA1USR for immunohistochemical detection of ribozymes in the tissues of mice which were administered two structurally different ribozymes has demonstrated its utility as a reagent for in vivo localization of ribozymes containing the 2(')-C-allyl uridine modification.

Ultrastructural immunogold cytochemistry with autoimmune human sera and an antibody to uridine implicate human mast cell granules in RNA biology

Human mast cells are professional secretory cells that store synthetic products in large granules filling their cytoplasm. Unlike many secretory cells, the principal synthetic organelle, ribosome-rich endoplasmic reticulum, is a minor component of their cytoplasm. Sightings of nonmembrane-bound ribosomes in and near their secretory granules stimulated detailed ultrastructural studies of various RNA species to implicate secretory-storage granules in RNA biology. In the work reported here, postembedding immunogold ultrastructural cytochemistry indicates that human mast cells contain uridine, an integral ingredient of RNA, and ribonucleoproteins, known to associate with small nuclear RNAs important for splicing RNA precursors, several ribonucleoproteins with possible functions in other aspects of RNA biology and ribonucleoproteins known to associate with ribosomes. These findings should catalyse future work toward establishing the full functional repertoire of secretory-storage granules.

Preparation and characterization of polyclonal and monoclonal antibodies specific for covalently linked DNA/RNA cross sections

Covalently linked cross sections refer to structures that mimic hydrogen-bonded purine-pyrimidine, purine-purine, and pyrimidine-pyrimidine duplexes. Cross sections dA [symbol:see text] U and A [symbol: see text] dT, which have been synthesized chemically, have molecular dimensions similar to purine-pyrimidine base pairs in a double helix. We propose that antibodies to such covalent cross sections might facilitate the study of the pathogenesis of specific diseases or of biochemical processes in which base pair involvement is suspected and/or demonstrated. We have made polyclonal antibodies against "A:U" and "A:T" cross sections by immunizing rabbits with dA [symbol: see text] U and A [symbol: see text] dT, each conjugated to keyhole limpet hemocyanin (KLH). The antibodies were found to be highly specific for the cross sections and to cross react minimally to single nucleosides. Hybridomas secreting monoclonal antibodies to "A:T" were then generated from spleen cells of mice immunized with A [symbol: see text] dT conjugated to KLH. The MAbs produced were also found to be highly specific for "A:T" among various nucleosides. In fact, the binding of most of the monoclonal antibodies to "A:T" was only partially inhibited by high concentrations of adenosine or thymidine. All monoclonal antibodies to "A:T" cross react, but with lower affinity, to "A:U." Selected MAbs showed greater inhibition of binding to "A:T"-BSA by A + T than by A or T alone.

Brequinar sodium inhibits interleukin-6-induced differentiation of a human B-cell line into IgM-secreting plasma cells

Brequinar sodium (BQR) has been shown recently to be a potent immunosuppressive agent. This property has been attributed to the capacity of BQR to inhibit de novo pyrimidine nucleoside biosynthesis and consequently, to blockade the synthesis both of DNA and RNA. The influence of this new immunosuppressant on lymphocyte function has not been fully characterized. To determine the potential efficacy of BQR for the control of antibody-mediated graft rejection, which is of particular significance in the context of xenotransplantation, we have examined the influence of the drug on interleukin-6-dependent IgM production by the human B-cell line, SKW 6.4. At concentrations up to 10 micrograms/ml, BQR did not affect concanavalin A (Con A)-induced human peripheral blood lymphocyte proliferation or IL-6 production by blood mononuclear leucocytes. In contrast, the drug was very effective in inhibiting IL-6-stimulated IgM production by SKW 6.4 cells, with an optimal inhibitory concentration of 0.3 microgram/ml. As expected, addition of exogenous uridine (0.1 mM), the precursor of uridine triphosphate (UTP), reversed the inhibitory effect of BQR on antibody production, while cytidine (0.1 mM) potentiated the inhibitory activity of the drug. It was further demonstrated that the inhibition of IgM production was unrelated to DNA synthesis, indicating that BQR may affect IL-6 signal transduction and IgM production in SKW 6.4 cells independent of any effect on cell proliferation.

Isolation and specificity of antibodies to uridine

Antibodies to uridine were produced in rabbits using a conjugate of uridine (periodate oxidized) and bovine serum albumin as immunogen. The specificity of the antibodies was studied by estimating the inhibition of the binding of 3H-uridine-trialcohol to the antibodies by various non-radioactive related compounds, using a nitrocellulose filter assay. The antibodies were 1500-fold more reactive to the uridine-trialcohol than the parent nucleoside. They bound 3H-RNA at homologous base residues. The hapten specific antibodies were purified by affinity chromatography on a uridine-AH-Sepharose column.

Introduction of antigenic determining 2,4-dinitrophenyl residues into 4-thiouridine, N3-(3-L-amino-3-carboxypropyl) uridine and tRNA-Phe from E. coli

The introduction of antigenic determining 2,4-dinitrophenyl residues into the rare ribonucleosides 4-thiouridine (1a), and N3-(3-L-amino-3-carboxypropyl) uridine (2) as well as into tRNA-Phe from E. coli has been investigated. Alkylation of 1a with omega-bromo-2,4-dinitroacetophenone (3b) gives S-(2,4-dinitrophenacyl)-4-thiouridine (5A). Applying the reaction to the 5'-monophosphate of 1a, 5b is formed, but this product decomposes at pH 7. However, acylation of 2 with 2,4-dinitrobenzoic acid N-hydroxysuccinimide ester (4b) leads to N3-[3-carboxy-3-L-(2,4-dinitrobenzamido)propyl]uridine (6) which is stable in aqueous solution. The latter reaction was used for the introduction of an antigenic determining 2,4-dinitrophenyl residue into tRNA-Phe from E. coli. The modified tRNA-Phe was isolated and by degradation of the molecule with RNase T2 and alkaline phosphatase the nucleoside derivative 6 was obtained and found to be identical with the synthetic product.

Immunochemical characterization of the anti-RNA antibodies found in scleroderma and systemic lupus erythematosus. II. Reactivity with hsa-coupled, uridine-containing, monophosphoric ribodinucleotides

Sera from patients with scleroderma have been found to have anti-RNA antibodies which react with human serum albumin (HSA)-coupled uridine and uridine monophosphate (UMP) and are inhibited by uracil, uridine and UMP. Scleroderma sera react uniformly with 5'-polyuridylic acid (poly(U)) and fail to react with polyadenylic, polyuridylic acid poly(A) - poly(U)) which is also indicative of their uracil specificity. Anti-RNA antibodies found in systemic lupus erythematosus (SLE) are immunochemically different from those found in scleroderma in that, instead of being uniformly specific to uracil, they are markedly heterogeneous and may react with uracil, uridine and/or UMP. SLE sera frequently react with poly(A) - poly(U), indicating also their ability to recognize the double helical structure of double-stranded RNA. Thirty-seven scleroderma and thirty-four SLE sera from as many patients with either of these conditions were tested against HSA-coupled, uridine-containing monophosphoric dinucleotides in an attempt to characterize further their anti-RNA antibodies. Scleroderma sera were found to react primarily with dinucleotides in which uridine was the base proximal to the carrier protein and, except for sera that also contained antibodies to adenosine which reacted with UpA, they failed to react with dinucleotides in which uridine was in a terminal position only. Reaction with dinucleotides in which uridine was proximal to the carrier protein could be inhibited by uracil but not by the corresponding terminal base. Some lupus sera were found to react with both dinucleotides that contain the same bases in opposite sequence, e.g. ApU and UpA, while others were found to react with only one of the sequences. They were also found to react more frequently with dinucleotides in which HSA was coupled to a base other than uridine, suggesting that the reaction is primarily due to anti-DNA antibodies. Because immunization with dinucleotides coupled to protein prepared by the same method we have used, yields higher specificity to the base attached to the carrier protein, our findings suggest that, in scleroderma, a single event, akin to that of immunization with a purified antigen, gives rise to the anti-RNA antibodies, whereas in systemic lupus erythematosus there is a considerably wider immunological aberration.

Uracil-specific anti-R.N.A. antibodies in scleroderma

Antibodies to single-stranded R.N.A. were found by counter immunoelectrophoresis in all of 40 sera from patients with scleroderma. These antibodies were specific to the uracil bases of R.N.A. Antibodies to R.N.A. were also found in 20 of 40 sera from patients with systemic lupus erythematosus (S.L.E.), but in none of forty controls. Antibodies to R.N.A. found in S.L.E. sera could be differentiated immunochemically from those found in scleroderma in that they were more heterogeneous and could react selectively with either uridine or uridine monophosphate. Antibodies ot D.N.A. were more frequent in S.L.E. than in scleroderma. That antibodies to D.N.A. are actually present in scleroderma and precipitin lines are not the result of cross reactivity with anti-R.N.A. antibodies is indicated by the finding that 10 of the 18 scleroderma sera which reacted with D.N.A. also reacted with thymidine, a base present in D.N.A. but not in R.N.A.