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Biomedical subjects

R E Thach

Publications and source records attributed to R E Thach.

At least 73 records · Page 4Linked to original sources
PubMed1974

The mechanism of viral replication. Structure of replication complexes of encephalomyocarditis virus.

The structure of the purified replicative intermediate of encephalomyocarditis virus was determined by electron microscopy. Approximately 80% of the replicative intermediate complexes were characterized by a filament of double-stranded RNA of widely variable length, which had a "bush" of single-stranded RNA at one end. In many examples one or more additional single-stranded bushes were appended internally to the double-stranded RNA filament. These results support the view that before deproteinization, replicative intermediate contains little if any double-stranded RNA.

Centrifugation, Density Gradient↗
PubMed1974

Encephalomyocarditis virus infection of mouse plasmacytoma cells. I. Inhibition of cellular protein synthesis.

Mouse plasmacytoma ascites tumor cells (MOPC 460) were efficiently infected with encephalomyocarditis virus. Inhibition of host protein synthesis was evident after 2 h and complete by 4 h postinfection. The mechanism by which virus infection results in inhibition of host cell protein synthesis was studied in vitro. Cell-free protein-synthesizing systems, prepared from uninfected and infected cells, were found to be equally active with respect to their abilities to translate cellular and viral mRNAs. The plasmacytoma cell-free system was also shown to be insensitive to the addition of double-stranded viral RNA. Host cellular mRNA was isolated from uninfected and infected cells. No difference in the amount or size distribution of the mRNA was detected. However, the mRNA from infected cells was translated only 46 to 49% as actively as that from uninfected cells. mRNA isolated from cells in which initiation of protein synthesis was inhibited with pactamycin was similarly inactivated. Simultaneous addition of viral RNA and cellular mRNA to the plasmacytoma cell-free system resulted in a complete suppression of the translation of the cellular message, whereas viral RNA was translated normally.

Amino Acids↗
PubMed1974

Encephalomyocarditis virus infection of mouse plasmacytoma cells. II. Effect on host RNA synthesis and RNA polymerases.

The effect of encephalomyocarditis virus infection of MOPC 460 mouse plasmacytoma cells on host RNA synthesis and RNA polymerases was investigated. Consistent with work performed in other virus host systems, rates of RNA synthesis appeared to be inhibited in infected cells, whereas RNA degradation appeared normal. These results were further extended with isolated nuclei, in which distinct RNA polymerase activities could be studied under conditions where problems with RNA turnover and endogenous nucleotide pool sizes were insignificant. Endogenous nuclear RNA polymerase II activity was inhibited early postinfection and at 1 to 2 h prior to endogenous RNA polymerase I plus III activity. However, the solubilized enzymes were fully active with exogenous DNA as template. In fact, the levels of RNA polymerases I, II, and III, isolated from infected cells and nuclei, were indistinguishable from levels in uninfected cells and nuclei at each stage of their partial purification procedure. The chromatographic properties of the enzymes on DEAE-Sephadex were also unaltered. Furthermore, the RNA synthetic activity of these isolated enyzmes, or of nuclei isolated from uninfected cells, was resistant to extracts of nuclei or of cytoplasmic fractions from infected cells. These results are discussed in terms of a possible inhibition of RNA synthesis in vivo at the level of transcription initiation.

Animals↗
PubMed1971

Damage to biological samples caused by the electron beam during electron microscopy.

A new method has been developed which measures directly the beam damage suffered by biological specimens in the electron microscope. This method involves the use of radioautography to measure specific radioactivity of labeled specimens, either exposed or unexposed to the beam. Using this technique, it has been found that macromolecular samples such as ribosomes and R17 virions are severely damaged during standard electron microscopic operations: from 15 to 40% of the mass of the sample may be lost in a 30 sec exposure to the beam.

Autoradiography↗
PubMed1971

Translocation of messenger RNA and "accommodation" of fMet-tRNA.

Messenger RNA is moved a distance of approximately three nucleotides in the 5' direction relative to the ribosome during the translocation of peptidyl-tRNA from the A to the P site. This movement is catalyzed by G factor and is dependent on the hydrolysis of GTP. In contrast, mRNA is not moved during the f(2)-catalyzed hydrolysis of GTP that is involved in the activation of ribosome-bound fMet-tRNA. This second type of GTP-dependent reaction has been named "Accommodation".

Carbon Isotopes↗
PubMed1970

A new protein synthesis factor from Escherichia coli.

A new factor that effects protein synthesis by Escherichia coli extracts was partially purified from the 1 M NH(4)Cl wash of E. coli ribosomes. This factor stimulates the binding of aminoacyl-tRNA to 30S ribosomes, and it increases the rate of synthesis of polyphenylalanine in the presence of 30S and 50S subunits.

Bacterial Proteins↗