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PubMed1976

Tirandamycin, an inhibitor of bacterial ribonucleic acid polymerase.

The antibiotic tirandamycin (a 3-acyltetramic acid structurally related to streptolydigin) specifically inhibits transcription by interfering with the function of bacterial ribonucleic acid polymerase. Ribonucleic acid polymerases from rat liver nuclei are not subject to tirandamycin inhibition. Qualitatively, the mode of action of the antibiotic is identical to that of streptolydigin in inhibiting chain initiation as well as chain elongation during the transcriptional process. However, tirandamycin is approximately 40 times less potent than streptolydigin. The structures of the 3-acyl groups of the two acyltetramic acid antibiotics tirandamycin and streptolydigin differ only slightly in the degree of oxidation of the terminal dioxabicyclo (3.1)nonane system and possess the same stereochemistry (D. J. Duchamp, A. R. Branfman, A. C. Button, and K. L. Rinehart, 1973). More significantly, major differences occur at the 1 and 5 positions of the tetramic acids. Tirandamycin contains no substituents; streptolydigin contains a substituted acetamide function at position 5 and a sugar moiety at position 1. The lack of substituents at the 1 and 5 positions of the tetramic acid portion in tirandamycin is probably responsible for the reduced biopotency of tirandamycin as compared with streptolydigin.

Animals↗
PubMed1972

Studies on Phytoalexins: The Relationship between Actinomycin D and Ribonucleic Acid Synthesis during the Induction of Phaseollin in the French Bean (Phaseolus vulgaris L.).

Actinomycin D stimulated phaseollin production in endocarp tissues of the French bean (Phaseolus vulgaris L.), maximum production being obtained with 25 to 30 micrograms per milliliter of antibiotic. Under these conditions, net incorporation of (3)H-uridine into total cell ribonucleic acid was inhibited by more than 80% over a 6-hour induction period. If allowance was made for a 2-hour lag in the action of actinomycin D, inhibition of incorporation was greater than 95%. Contrary to other reports, no evidence was obtained of an increased formation of any specific ribonucleic acid fraction. Actinomycin D applied in the cold (4 C) was not found to be effective in stimulating phaseollin production. When applied in this way, actinomycin D did not affect induction of phaseollin by a fungal peptide, Monilicolin A, although ribonucleic acid synthesis was inhibited by more than 95%. It is suggested that the induced formation of phytoalexins may not be dependent on increased ribonucleic acid synthesis as has previously been claimed.Other experiments indicated that the apparent effects of actinomycin D on ribonucleic acid synthesis could be influenced by the choice of precursor used to label ribonucleic acid and by the order of addition of precursor and antibiotic to the plant tissue. These effects were only observed in the period immediately following application of actinomycin D. It is suggested that such effects could critically influence the results obtained in short term experiments and may explain some differences in reported action of actinomycin D from different laboratories.

Journal Article↗
PubMed1998

Regulation of hypothalamic arginine vasopressin messenger ribonucleic acid and pituitary arginine vasopressin content in fetal sheep: effects of acute tonicity alterations and fetal maturation.

OBJECTIVE: Fetal arginine vasopressin contributes to fetal and amniotic fluid homeostasis by increasing water resorption in the kidney and, at higher plasma levels, circulatory homeostasis by vasopressor effects. In utero and neonatal exposure of rat pups to prolonged alterations in plasma osmolality may permanently alter (imprint) pituitary arginine vasopressin content and adult responses to osmotic challenges. Our objective was to investigate fetal developmental changes and the impact of maternal dehydration and maternal hyponatremia on fetal pituitary arginine vasopressin content and hypothalamic arginine vasopressin messenger ribonucleic acid expression. STUDY DESIGN: Ten pregnant ewes with singleton fetuses (135 +/- 1 day) were chronically prepared with maternal vascular catheters. Ewes were assigned to receive water deprivation (n = 4) [desamino, D-Arg8]-arginine vasopressin-induced plasma hyponatremia (n = 3), or 4 days of observation (n = 3). Three additional pregnant ewes with preterm (110 +/- 1 day) singleton fetuses were also included for a study of maturational effects. Daily maternal blood samples were analyzed for determination of plasma arginine vasopressin, electrolytes, and osmolality. After the study protocol, fetuses were operatively delivered, umbilical blood samples obtained, and fetuses put to death for pituitary and hypothalamic tissues. Pituitary arginine vasopressin content was determined by radioimmunoassay, and hypothalamus arginine vasopressin messenger ribonucleic acid expression was detected by Northern blotting. RESULTS: Dehydration significantly (P < .05) increased, and hyponatremia significantly decreased maternal plasma sodium concentration compared with controls. Fetal plasma sodium concentration significantly changed in parallel with maternal values (dehydration: 139 +/- 1 to 150 +/- 1 mEq/L; hyponatremia: 138 +/- 1 to 128 +/- 5 mEq/L). Fetal hypothalamic arginine vasopressin messenger ribonucleic acid expression and pituitary content did not change in relation to these relatively acute alterations in plasma tonicity. However, among all animals, arginine vasopressin messenger ribonucleic acid expression was significantly negatively correlated with pituitary arginine vasopressin content (r2 = 0.563; P = .02). Arginine vasopressin messenger ribonucleic acid expression was significantly lower in both preterm and near-term fetuses (P < .05) than that in the maternal ewe, although pituitary arginine vasopressin content (in micrograms per milligram of protein) was significantly greater in preterm fetuses (P < .01, vs maternal; P < .05, vs near term). CONCLUSIONS: The significant inverse relation between arginine vasopressin content and arginine vasopressin messenger ribonucleic acid suggests a dynamic arginine vasopressin synthesis-content feedback relationship is functional in the near-term fetus. Although relatively acute periods of maternal hypertonicity or hypotonicity do not alter fetal pituitary arginine vasopressin content or hypothalamic arginine vasopressin messenger ribonucleic acid expression, longer-term plasma tonicity alterations may potentially have an impact on the fetal arginine vasopressin hypothalamic-pituitary axis.

Animals↗
PubMed1992

Messenger ribonucleic acid for transforming growth factor-alpha, but not for epidermal growth factor, is expressed in fetal and neonatal mouse brain.

OBJECTIVE: Little is known concerning the presence of transforming growth factor-alpha in fetal and neonatal tissues. Our objective was to analyze messenger ribonucleic acid expression for transforming growth factor-alpha and epidermal growth factor, the structural and biochemical analog of transforming growth factor-alpha in fetal and neonatal murine brain. STUDY DESIGN: Messenger ribonucleic acid was prepared from whole brains of mice from these developmental stages: embryonic days 14, 15, and 17, postnatal days 0, 4, 10, and adult. Polymerase chain reaction was performed on the complementary deoxyribonucleic acid obtained from reverse transcription of messenger ribonucleic acid with transforming growth factor-alpha and epidermal growth factor primers. In addition, ribonuclease protection assay was used to identify transforming growth factor-alpha transcripts. RESULTS: We found messenger ribonucleic acid encoding transforming growth factor-alpha in all stages of development used. Epidermal growth factor messenger ribonucleic acid was not found in any stage. Ribonuclease protection assay confirmed transforming growth factor-alpha transcripts in these tissues. CONCLUSION: Transforming growth factor-alpha may play an autocrine or paracrine role in the differentiation or maintenance of murine fetal and neonatal brains.

Aging↗
PubMed1981

Synthesis of a nitrobenzeneboronic acid substituted polyacrylamide and its use in purifying isoaccepting transfer ribonucleic acids.

Highly purified isoaccepting species of transfer ribonucleic acid (tRNA) were prepared by use of a polyacrylamide substituted with nitrobenzeneboronic acid functional groups. This method exploits the well-known ability of boronic acids to complex with RNA cis-diols. tRNA isoacceptors were obtained by enzymatically acylating a mixture of tRNA species with a single amino acid and passing the mixture over a solid-state nitrobenzeneboronic acid at pH 6.5 or 7.0. Pure aminoacyl-tRNA eluted at the column liquid volume, and unacylated tRNA species were bound. The bound species were recovered by lowering the pH of the eluant to 4.5. This procedure is uncomplicated, rapid, and applicable to nearly all tRNA isoacceptors. It does not chemically modify the tRNA(s) of interest or adversely affect their ability to be aminoacylated. Since boronic acids must be ionized to complex with cis-1,2-diols, boronic acid derivatives were prepared which ionize at a pH compatible with the stability of the aminoacyl bond. Two isomeric benzeneboronic acids with pKas of 6.8 and 7.4 were synthesized by introducing electron-withdrawing nitro groups into the aromatic ring. The addition of succinyl side chains permitted the nitrobenzeneboronic acids to be coupled to aminoethylpolyacrylamide. The properties of the nitrobenzeneboronic acid substituted acrylamide were illustrated by enriching phenylalanyl-tRNA at pH 7.0 to greater than 95% purity (1.63 nmol of phenylalanine accepted per A260 unit of tRNA) and seryl-tRNA isoacceptors at pH 6.5 to essentially theoretical purity (1.58 nmol of serine accepted per A260 unit of tRNA.

Acrylic Resins↗
PubMed1971

Characterization of ribonucleic acid from visna virus.

A single-stranded ribonucleic acid(s) has been isolated from purified virions of visna virus. It consists of two major components, namely 63S and "4S," under the conditions employed for ribonucleic acid (RNA) extraction. The 63S component can be converted to subunits by heat and dimethylsulfoxide treatments. Analyses by base composition indicate that the "4S" RNA isolated from visna virus is not a random breakdown product of the 63S component as a result of extraction, nor is it randomly derived from cellular RNA.

Animals↗
PubMed1993

Expression of messenger ribonucleic acid for epidermal growth factor receptor and its ligands, epidermal growth factor and transforming growth factor-alpha, in human first- and second-trimester fetal ovary and uterus.

OBJECTIVES: The epidermal growth factor receptor, a 170 kd polypeptide with tyrosine kinase activity, is used as the common receptor by two homologous polypeptide growth factors, epidermal growth factor and transforming growth factor-alpha. The activation of the epidermal growth factor receptor results in effects including deoxyribonucleic acid synthesis and cellular differentiation. Epidermal growth factor, transforming growth factor-alpha, and the epidermal growth factor receptor are reported to be associated with adult reproduction. However, the pattern of gene expression for the epidermal growth factor receptor and its ligands in human fetal reproductive tissues has not been detailed previously. STUDY DESIGN: We studied the expression of messenger ribonucleic acid encoding three polypeptides, epidermal growth factor receptor, epidermal growth factor, and transforming growth factor-alpha, in 10-, 15-, 19-, and 22-week human fetal ovaries and uteri. Ribonucleic acid was prepared from the fetal tissues and made into complementary deoxyribonucleic acid by reverse transcription. The complementary deoxyribonucleic acid was amplified by polymerase chain reaction, using primers specific for the human epidermal growth factor receptor, epidermal growth factor, and transforming growth factor-alpha. RESULTS: We found that epidermal growth factor receptor messenger ribonucleic acid was present in all stages of ovarian and uterine tissues studied. In addition, both epidermal growth factor and transforming growth factor-alpha messenger ribonucleic acid was found in all four stages of ovarian development. Epidermal growth factor messenger ribonucleic acid was detected in all four stages of fetal uterine development. CONCLUSIONS: This is the first demonstration, to our knowledge, of epidermal growth factor receptor, epidermal growth factor, and transforming growth factor-alpha messenger ribonucleic acid expression in human first- and second-trimester uterus and ovary.

Base Sequence↗
PubMed1973

Evidence for the existence of two arginyl-transfer ribonucleic acid synthetase activities in Escherichia coli.

Two arginyl-transfer ribonucleic acid (tRNA) synthetase (EC 6.1.1.13, arginine: ribonucleic acid ligase adenosine monophosphate) activities were found in extracts of Escherichia coli strains AB1132 and NP2. The two arginyl-tRNA synthetase activities in extracts of strain AB1132 were found to be separable by diethylaminoethyl-cellulose column chromatography, Sephadex column fractionation, and by sucrose density gradient centrifugation. In addition, in the standard assay using extracts of strain AB1132 there were two pH optima for arginyl-tRNA synthetase activity. Furthermore, when arginyl-tRNA synthetase of strain NP2 was fractionated by hydroxylapatite column chromatography, two activities were observed which were similar to those of strain AB1132.

Amino Acyl-tRNA Synthetases↗
PubMed1997

Transient expression of alpha-1B adrenoceptor messenger ribonucleic acids in the rat superior cervical ganglion during postnatal development.

We have examined the developmental profile of the alpha-1 and alpha-2 adrenergic receptor messenger ribonucleic acids expression in the rat superior cervical ganglion. The expression of the six messenger ribonucleic acids was studied using reverse transcription-polymerase chain reaction. At four weeks, the dominant messenger ribonucleic acids transcripts in this sympathetic ganglion were alpha-1C, alpha-2A, alpha-2B and alpha-2C. The expression of alpha-1 genes in the superior cervical ganglion appears to be regulated during postnatal development in that two alpha-1 (alpha-1B, alpha-1C) genes were expressed at birth, three, seven and 14 days postnatal but no amplified product for alpha-1B was detected at 28 days and in the aged animals, while the alpha-1C transcript continued to be expressed. No amplified product for alpha-1D was detected in superior cervical ganglion at any of the ages studied. While all three alpha-2 genes were expressed in the superior cervical ganglion at four weeks the dominant alpha-2 messenger ribonucleic acids transcript expressed in the superior cervical ganglion was alpha-2A. This pattern of alpha-2 adrenoceptor gene expression was maintained from birth, throughout development and into old age. These results suggest that the expression of alpha-1 adrenergic receptors in the superior cervical ganglion is regulated developmentally while the expression of alpha-2 genes remains unchanged.

Aging↗
PubMed1999

Effect of human seminal fluid on production of messenger ribonucleic acid for metalloproteinase 2 and metalloproteinase 9 in cervical epithelial carcinoma cells.

OBJECTIVES: The risk for cervical cancer is related to sexual intercourse. One factor associated with tumor invasion and metastases is the production of matrix metalloproteinases, which degrade the extracellular matrix. The ability of human semen to influence production of messenger ribonucleic acid for 2 matrix metalloproteinases associated with cervical cancer, MMP-2 and MMP-9, was examined. STUDY DESIGN: Seminal fluids from 16 men were diluted 1:50 and incubated with the cervical carcinoma cell line HeLa for 18 hours. Cells were harvested, ribonucleic acid was isolated and reverse transcribed into complementary deoxyribonucleic acid, and deoxyribonucleic acid sequences coding for regions of the genes for MMP-2 and MMP-9 were generated by polymerase chain reaction and detected by enzyme-linked immunosorbent assay. RESULTS: All 16 semen samples inhibited production of MMP-2 messenger ribonucleic acid. The MMP-2 messenger ribonucleic acid synthesis in the presence of semen was a mean of 39.5% of the control value. In contrast, MMP-9 messenger ribonucleic acid synthesis was stimulated (mean stimulation, 68.3%) by semen in 10 of the 15 samples tested. Synthesis of beta-actin was comparable in each culture, and cell viability was unaffected by the diluted semen. CONCLUSION: The capacity of semen to influence transcription of the genes for matrix metalloproteinases may be one mechanism whereby sexual activity influences cervical cancer progression.

Actins↗
PubMed1977

Transient rates of synthesis of five amionacyl-transfer ribonucleic acid synthetases during a shift-up of Escherichia coli.

The steady-state levels of a number of aminoacyl-transfer ribonucleic acid synthetases are known to be positively correlated with growth rate in Escherichia coli. To describe the regulation of these enzymes during a nutritional shift-up, use was made of the recent identification of polypeptide chains of several synthetases in whole cell lysates resolved by the O'Farrell two-dimensional gel system. A culture growing in acetate minimal medium was shifted to glucose-rich medium and pulse labeled with [3H]leucine and [3H]isoleucine for 30- or 6-s intervals during the 20 min after the shift. After mixing with a uniformly [35S]sulfate-labeled reference culture, the samples were subjected to two-dimensional gel electrophoresis. The 3H/35S ratio in the resolved synthetase polypeptides provided an accurate estimation of their transient rates of synthesis. Five aminoacyl-transfer ribonucleic acid synthetases (those for argnine, glycine, isoleucine, phenylalanine, and valine) exhibited an increase in formation within 30 to 90 s after the shift-up. The magnitude of the increases corresponded to the final steady-state values and were reached within 2 to 3 min. The addition to rifampin revealed that the increase in the differential rate of valyl-transfer ribonucleic acid synthetase formation was the result of increased messenger ribonucleic acid transcription and not of a relaxation of some translation restriction.

Acetates↗
PubMed1967

Effect of ethylenediaminetetraacetic acid-Tris(hydroxymethyl)aminomethane on release of the acid-soluble nucleotide pool and on breakdown of ribosomal ribonucleic acid in Escherichia coli.

Brief treatment of Escherichia coli with 2 x 10(-4)m ethylenediaminetetraacetic acid (EDTA)-0.12 m tris(hydroxymethyl)aminomethane (Tris), pH 8.0, or 0.12 m Tris alone resulted in the release of the acid-soluble nucleotide pool at 3 or 23 C. Exposure to EDTA-Tris for up to 90 min at 3 C did not result in the release of increasing amounts of 260-mmu-absorbing material. At 23 and 37 C, EDTA-Tris resulted in a steady increase in acid-soluble 260-mmu-absorbing material. Previous growth environment did not alter the release. There appeared to be degradation of 23S ribonucleic acid (RNA) after 10 min of exposure at 23 C. In addition, there was degradation of nucleotides to nucleosides and bases. This occured either within the cells with altered permeability or in the periplasmic space. This occurred in the presence of EDTA and Tris but was not seen with EDTA-phosphate. The mechanism of this degradation is unclear, since it occurs in ribonuclease I-deficient strains. Exposure to Tris buffer for long periods of time at 23 C resulted in release of the nucleotide pool and in degradation of RNA and nucleotides. These studies point out that the EDTA-Tris effect on E. coli must be divided into two parts, an early (4 to 5 min) change in permeability and a later phase of actual RNA breakdown and nucleotide degradation. Studies utilizing EDTA and Tris as agents altering permeability must thus be viewed with caution. Although the cells are viable, they have lost their acid-soluble nucleotide pool and have undergone degradation of some ribosomal RNA.

Buffers↗
PubMed1952

Phage formation in Staphylococcus muscae cultures. X. The relationship between virus synthesis, the release of bacterial ribonucleic acid, virus liberation, and cellular lysis.

1. Under a variety of conditions in which cells are infected with one or a few virus particles and the host cells are killed, but no infective particles or virus material is formed as indicated by plaque count, one-step growth curve, or protein or desoxyribonucleic determinations, the cells neither lyse nor release ribonucleic acid into the medium. 2. The "killing" effect of S. muscae phage is separate from its lytic property. 3. The release of ribonucleic acid into the medium is not simply due to the killing of the cell by the virus, and ribonucleic acid is never found in the medium unless virus material is synthesized. 4. Infected cells of S. muscae synthesizing virus release ribonucleic acid into the medium before cellular lysis begins and before any virus is liberated. 5. The higher the phage yield the more ribonucleic acid is released into the medium before any virus is released. 6. Phage may be released from one strain of Staphylococcus muscae without cellular lysis, although bacterial lysis begins shortly after the virus is released. In another strain, infected under similar conditions, virus liberation occurs simultaneously with cellular lysis. 7. The viruses liberated from both bacterial strains appear to be the same in so far as they cannot be distinguished by serological tests, have the same plaque type and plaque size, and need the same amino acids added to the medium in order to grow. Furthermore, the virus liberated from one strain can infect and multiply in the other strain and vice versa. 8. It is suggested that virus synthesis, in S. muscae cells infected with one or a few phage particles, leads to a disturbance of the normal cellular metabolism, resulting in lysis of the host cell.

Bacteriophages↗
PubMed1994

Influence of slight sequence changes on the free energy of a single stranded ribonucleic acid molecule.

Single-stranded ribonucleic acid molecules take a variety of secondary structures. The free energy (g) of a given secondary structure of a molecule is calculated from the Boltzmann weighted summation over the states of this molecule taking this secondary structure. Likewise, the free energy (G) of a molecule is calculated from the summation over the states of this molecule, which takes various secondary structures. The g-value can be evaluated by Salser's method (1977, Cold Spring Harbor Symp. Quantum Biol. 42, 985-1002). By use of these values, the G-value can also be obtained. Computer studies utilizing this method reveal that there is a particular class of molecules whose G-values tend to increase when the sequences are slightly changed. As far as we examined, such molecules take few secondary structures that fulfill the following two conditions simultaneously: (i) The g-value is close to that of the optimal secondary structure. (ii) The structure is very different from the optimal secondary structure. Here, the optimal secondary structure means the one with the lowest g-value among all the secondary structures taken by the molecule.

Base Sequence↗
PubMed1993

The regional distribution of thyrotropin-releasing hormone receptor messenger ribonucleic acid in the brain.

Messenger ribonucleic acid (mRNA) from mouse brain was reversely transcribed and complementary deoxyribonucleic acid (cDNA) encoding transmembrane domains (TM) 3 through TM6 of the thyrotropin-releasing hormone receptor (TRH-R) could be amplified by polymerase chain reaction (PCR). The partial cDNA of TRH-R was identical to that of the pituitary in size and sequence. The regional distribution of reverse transcription PCR products (partial cDNA of TRH-R) was similar to that of TRH-Rs themselves, except in cerebellum where TRH-R mRNA levels were relatively higher than the levels of TRH-Rs themselves previously reported.

Animals↗
PubMed1976

Isolation and characterization of purified rat casein messenger ribonucleic acids.

Purification of casein messenger ribonucleic acids (mRNAs) from lactating rat mammary gland RNA has been accomplished by a combination of sizing techniques, including Sepharose 4B chromatography and preparative agarose-urea gel electrophoresis, and affinity chromatography of poly(adenylic acid)-containing mRNA on oligo(dT)-cellulose. The separation of the individual casein mRNAs into discrete molecular species free of apparent ribosomal RNA contaminants was facilitated by the use of denaturing conditions either prior to or during each of the fractionation procedures. Two casein mRNA fractions were isolated: (1) a 15S mRNA doublet which directed the synthesis of the two largest rat caseins in the wheat-germ, cell-free, translation assay, and (2) a 12S mRNA which migrated as a single species during agarose-urea gel electrophoresis and directed the in vitro synthesis of the smallest of three rat caseins. These mRNAs had apparent molecular weights of 450 000 +/- 30 000 and 320 000 +/- 25 000 and contained poly(adenylic acid) sequences at their 3' termini ranging from 15 to 150 residues with number average lengths of 42 and 38 adenosines, respectively. The purity of the isolated casein mRNA'S was determined both by agarose-urea gel electrophoresis and by a careful comparison of the total products synthesized in the wheat-germ translation assay with those recognized by a specific casein antibody using an indirect immunoprecipitation technique. The specificity of the indirect immunoassay procedure was demonstrated by the selective displacement by purified rat casein of greater than 95% of the radioactive product synthesized in the cell-free system. Under optimal translation conditions for casein mRNA, at least 90% of the released protein synthesized in response to the 15S casein mRNA was specifically immunoprecipitable, representing a 178-fold purification compared with the initial RNA extract. Using these techniques a comparable purification was also obtained for a 15S mouse casein mRNA fraction. Finally, an analysis by fluorography on 5-20% (w/v) polyacrylamide gradient slab gels of the total proteins synthesized in response to both the 15S and 12S casein mRNAs revealed a close correspondence with those proteins which were specifically immunoprecipitated.

Animals↗
PubMed2005

DNA recognition and recognition control of alpha-peptide ribonucleic acids by external factors.

Peptide ribonucleic acid (PRNA) is one of artificial nucleic acids, which enables us to control its nucleobase orientation and recognition behavior by external factors through the synergetic effects of reversible borate ester formation and intramolecular hydrogen bond formation. In this study, a series of novel alpha-PRNA oligomers, possessing alternative alpha-PRNA/basic amino acid sequences, were newly designed, synthesized, and evaluated as the second-generation PRNA. As expected, these alpha-PRNAs indeed formed highly stable sequence-specific complexes with the complementary DNAs, for which both the conventional hydrogen-bonding interactions between the complementary nucleobase pairs and the electrostatic interactions between the basic amino acid's ammonium cation and the DNA's phosphate anion on the backbone are jointly responsible.

Buffers↗
PubMed1970

Characterization of rapidly labeled ribonucleic acid from dwarf peas.

The ribonucleic acid synthesized by excised shoots of dwarf pea (Pisum sativum L. cv. Progress No. 9) during short labeling periods has been characterized. Thirty percent of the total (32)P(i) incorporated in 1 hour is found in the ribosomal fraction. This labeled RNA was polydisperse (6-18 Svedberg units) and after chromatography on a methylated albumin-kieselguhr column about 80% of the radioactivity appeared in two peaks. One of these appeared on the shoulder of heavy ribosomal RNA ("mRNA") while the other was tenaciously bound to the column (TB-RNA). In the presence of high NaCl concentration, about half of the polydisperse RNA interacted with ribosomal RNA and eluted as "mRNA" while the remainder eluted as TB-RNA. This interaction in the presence of salt seems to result in the alteration of secondary structure because the "mRNA" fraction had a high sedimentation coefficient (45-50 Svedberg units). The polydisperse RNA approaches DNA in low cytidylate and guanylate content. After short periods of labeling TB-RNA showed higher adenylate content than "mRNA." The radioactivity from the "mRNA" peak can be chased, and these counts may represent a class of shortlived messenger RNA molecules with an average half-life of 10 to 15 minutes. The other component, TB-RNA, could not be chased and accumulated radioactivity during the chase period.

Centrifugation, Density Gradient↗