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Biomedical subjects

T Sreevalsan

Publications and source records attributed to T Sreevalsan.

36 records · Page 2Linked to original sources
PubMed1979

Sindbis virus RNA replication. I. Properties of the 38s RNA species.

Four species of single-stranded virus RNA (49S, 38S, 33S and 26S) were detected in chick embryo fibroblasts infected with Sindbis virus. The relative amounts of these RNAs were unaffected by the m.o.i. There was also no significant difference in the molar proportions of the four RNA species when purified virion RNA was used as the inoculum. These findings suggest that the 38S and 33S species represent products of the transcription of non-defective virion RNAs. Kinetic analyses of RNA synthesis indicated that during a 1 min pulse more radioactivity was associated with the 38S than with the 49S RNA and as the length of the pulse increased, the ratio of 38S/49S decreased, with the 49S appearing as the predominant species. Furthermore, addition of cycloheximide within the first 3 h p.i. resulted in detection of only the 49S species. Synthese of all four species was unaffected when the drug was added after this time period. These data suggest that the 38S species may represent newly synthesized 49S molecules and some protein(s) synthesized within the first 3 h p.i. is necessary for maintaining the 38S conformational form.

Animals↗
PubMed1975

Studies on the intracisternal A-type particles in mouse plasma cell tumors: induction of maturation of the particles.

Maturation of the intracisternal A-type particle found in two mouse plasma cell tumors was induced by treating the cells in culture with IDU-DMSO or with DMSO only. Morphologically, the mature particles with electron-dense nucleoids closely resembled the mature particles described in human tumor cell lines treated in a like manner. They also closely resembled the virus that has been described in guinea pig leukemias. It was not possible to demonstrate infectivity of the mature particle, as latent intracisternal A-type particles induced by IDU were found in the mouse cells presumed to be free of virus. The biochemical studies did not show distinct new peaks of virus-specific particles in sucrose density gradients when the particles in the treated cells were compared with the particles of the untreated cells. There was a difference in the density of the particles observed in the induced cells (1.2) and those of the control cells (1.185). This may reflect the difficulty of separating mature and immature particles. Analysis of the RNA present in the particles showed that the ratio of heavy-molecular-weight RNA in activated cells to the predominant species (21S) is much greater than that in control cells. Detectable levels of enzyme activity were not found in the induced particles. This could be due to too low a concentration of particles in the preparations.

Animals↗
PubMed1975

Inhibitory effects of lipophilic acids and related compounds on bacteria and mammalian cells.

The inhibitory effect of lipophilic acids, antimicrobial food additives, and analgesics-antipyretics was examined at concentrations from 0.1 to 100 mM in bacteria (Bacillus subtilis and Escherichia coli) and mammalian cells (HeLa, human fibroblasts, and mouse neuroblastoma cells). Most compounds inhibit the growth of HeLa cells about as efficiently as that of B. subtilis. However, butyrate and propionate, as well as acetaminophen, antipyrene, phenacetin, and salicylamide, inhibit HeLa at millimolar concentrations whereas, at least 10 times higher concentrations are needed to inhibit B. subtilis. The concentrations needed to inhibit growth by 50% decrease with increasing octanol-water partition coefficients of the compound. Growth of E. coli is inhibited similar to that of B. subtilis by all compounds except butylbenzoate, decanoate, and linoleate which cannot penetrate the lipopolysaccharide layer. All growth inhibitors inhibit amino acid uptake into bacteria and their vesicles, and oxygen consumption in bacteria. In HeLa cells or human fibroblasts, neither amino acid uptake nor adenine 5'-triphosphate synthesis are inhibited by fatty acids at concentrations that completely inhibit growth. Short chain fatty acids (propionate, butyrate, and pentanoate) induce in HeLa the formation of cell processes. In neuroblastoma cells, grown in the presence of 10% fetal calf serum, butyrate also induces such processes which slowly continue to grow in length for at least 7 days; these processes differ in speed of formation, width, and cycloheximide susceptibility from the thin processes produced by serum deprivation alone.

Bacteria↗
PubMed1974

Proteins specified by Sindbis virus in HeLa cells.

HeLa cells infected with Sindbis virus were found to contain five species of nonvirion proteins besides the structural proteins of the virus. Some of the nonvirion proteins were found to serve as precursors to the viral structural proteins in a pulse-chase experiment.

Carbon Radioisotopes↗
PubMed1973

Growth inhibition and morphological changes caused by lipophilic acids in mammalian cells.

Human (HeLa, Chang liver, L-132, and Intestine 407) and other mammalian (XC, SV3T3, and chick-embryo) cells in tissue culture are at least as sensitive to inhibition by lipophilic acids and nitrite as bacteria. Some of these compounds are the most frequently used antimicrobial food additives. Short-chain fatty acids (up to hexanoate) and parabens induce, at partially inhibitory concentrations, a jagged cell shape in continuous epithelial-like cell lines, such as HeLa, Chang liver, L-132, and Intestine 407. This morphological effect is not mediated or enhanced by butyryl cyclic AMP, which specifically affects fibroblasts.

Animals↗
PubMed1973

Viral RNAs associated with ribosomes in Sindbis virus-infected HeLa cells.

Virus specific RNA ribosome complexes were isolated by sucrose density gradient centrifugation of cytoplasmic extracts from HeLa cells infected at 42 C with an RNA(+) mutant (ts2) of Sindbis virus. Viral RNA-ribosome complexes were accumulated by infected cells treated with sodium fluoride and cycloheximide. The RNA-ribosome complexes were characterized by (i) their sensitivity to the action of ribonuclease or ethylenediaminetetraacetic acid, (ii) their density in cesium chloride gradients, and (iii) presence of host ribosomes and viral RNAs. The viral RNAs were isolated and characterized. The results showed that two species of single-stranded RNAs (a 28s and 18 to 15s species) were associated with the complexes. Base composition analysis of the viral RNAs indicated that both species had a higher adenine content than the 42s or 26s forms of viral RNAs. The RNAs associated with the ribosome complexes were virus specific since they annealed with denatured double-stranded RNAs from the infected cells. Little or no 42S RNA was associated with the RNA-ribosome complexes. The results suggest that the 28s and 18 to 15s forms of RNAs may represent viral messenger RNAs.

Adenine↗
PubMed1970

Membrane binding of input arbovirus ribonucleic acid: effect of interferon or cycloheximide.

By 1 hr after infection, 36% of input Semliki Forest virus ribonucleic acid (RNA) which was cell associated was found in a membrane structure. This structure had many similarities to the membrane-associated replication complex (MRC) which had previously been identified in arbovirus infections. Interferon treatment did not affect the association of viral RNA with the MRC structure, but cycloheximide treatment inhibited it.

Animals↗
PubMed1970

Association of viral ribonucleic acid with cellular membranes in chick embryo cells infected with Sindbis virus.

Membranes from cells infected with Sindbis virus had associated with them viral ribonucleic acid (RNA) polymerase and about 60 to 70% of the viral RNA labeled when short pulses were used. This RNA contained most of the replicative intermediate and replicative form of viral RNA found in the infected cells. The use of "Mg(2+) sarkosyl crystals" permitted the isolation of membrane-bound nucleic acids and allowed the demonstration that Sindbis virus RNA was synthesized on a membrane-viral RNA complex. Viral RNA from the infecting virions first became associated with the membranes during the latent period and, subsequently, slowly detached. The attachment of the viral RNA to the membranes did not require active viral RNA polymerase, since RNA from ts6, an RNA(-) temperature-sensitive mutant of Sindbis virus, associated with cellular membranes at a nonpermissive temperature. However, the subsequent detachment of the RNA from the membranes was restricted in the absence of viral RNA synthesis. The results indicate that association of viral RNA with cellular membranes may represent an early step occurring during the replication of Sindbis virus RNA.

Amino Acids↗
PubMed1969

Sindbis virus-induced viral ribonucleic acid polymerase.

A cytoplasmic structure containing the viral ribonucleic acid (RNA) polymerase has been isolated by sucrose density centrifugation from cells infected with Sindbis virus. Uninfected cells did not contain any such structure. Preliminary experiments indicated that the structure may be associated with membranes. This structure incorporated (3)H-guanosine triphosphate in vitro in the absence of added template. The RNA synthesized in vitro by the enzyme consisted of single-stranded 40S RNA, the ribonuclease-resistant replicative form, and possibly the replicative intermediate form of viral RNA. The products formed in vitro by the enzyme are identical in sedimentation rates to those formed in the infected cells in vivo.

Animals↗
PubMed1968

Replication of Western equine encephalomyelitis virus. II. Cytoplasmic structure involved in the synthesis and development of the virions.

Analysis of the cytoplasmic fraction of chick embryo cells during the exponential phase of Western equine encephalomyelitis (WEE) virus growth showed that the viral ribonucleic acid (RNA) labeled by a short pulse with (3)H-uridine was associated with a structure which sedimented in sucrose density gradients with a coefficient of 65S. The RNA extracted from this structure sedimented in sucrose density gradients at 26S. After a longer period of exposure to (3)H-uridine, the radio-active viral RNA was associated with a structure which sedimented in sucrose density gradients as would materials with coefficients of about 140S. The 140S structure contained viral RNA and viral protein. It was shown that the 140S structures are not virus-induced polysomes. The 140S structure contained predominantly the 40S type of viral RNA and some 26S type. Electrophoretic analysis of the disrupted virion revealed that at least two proteins (types I and II) were present in the purified virion. Only type II protein was present in the 140S structure. Unlike the virion, the 140S structure did not contain any lipid which could be detected by the incorporation of (14)C-choline. These data suggest that the 140S structure represents the internal nucleoprotein part of the virion. The rate of appearance of labeled virus lags behind that of the formation of the 140S structure in infected cells. Pulse-chase experiments with (3)H-leucine suggest that the 140S structure may represent a precursor to the virus particle. The results are discussed in terms of the maturation of WEE virus in the infected cells.

Acrylates↗
PubMed1968

Replication of Western equine encephalomyelitis virus. I. Some chemical and physical characteristics of viral ribonucleic acid.

The ribonucleic acid (RNA) from Western equine encephalomyelitis (WEE) virions sedimented through sucrose gradients with a sedimentation coefficient of 40S. Another viral RNA which was always associated with infected cells possessed a sedimentation coefficient of 26S. Both 40S and 26S RNA had identical base compositions and densities. The 40S RNA displayed a hyperchromic effect when heated with a T(m) of 57.5 C. When 40S RNA was heated at 90 C and cooled rapidly, it sedimented with a coefficient of 26S. Dialysis of 40S RNA against distilled water changed its sedimentation coefficient to 26S. The presence of 8 m urea or 50% dimethyl sulfoxide in the gradients also altered the sedimentation rate of 40S RNA to 26S. In the latter case, the 26S RNA retained 10% of the infectivity originally added as 40S RNA. Dialysis of 26S RNA against 0.5 m NaCl or 0.05 m acetate buffer at pH 4.0 altered it so that about 50% of the radioactivity sedimented with a coefficient of 40S. Chromatography on methylated albumin-kieselguhr columns failed to separate 40S RNA from 26S RNA. Viral RNA either exists in two conformations which sediment differently in sucrose or contains an extremely labile portion near the center and is easily broken into two equal pieces.

Arboviruses↗