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Biomedical subjects

S S Thach

Publications and source records attributed to S S Thach.

8 recordsLinked to original sources
PubMed1976

Competition between cellular and viral mRNAs in vitro is regulated by a messenger discriminatory initiation factor.

Encephalomyocarditis viral RNA has previously been shown to outcompete host cellular mRNA has for translation in vitro in crude and fractionated protein synthesizing systems. In the present communication it is shown that the competition is regulated by an initiation factor or complex of factors, and not the 40S initiation complex per se. The factor primarily involved is the murine equivalent of a component present in a partially purified preparation of rabbit initiation factor M3. Both the murine and rabbit factors are clearly messenger discriminatory.

Animals↗
PubMed1976

Relationships between intracisternal type A and extracellular oncornavirus-like particles produced in murine MOPC-460 myeloma cells.

Oncornavirus-like particles of the "A" (both intracisternal and intracytoplasmic) and "B" or "C" (extracellular) types are produced by murine MOPC-460 myeloma cells. This communication describes a comparative study on tracisternal A and extracellular particles. Both types of particles contain an RNA-dependent DNA polymerase activity, traces of 35S and 70 S RNA in addition to larger amounts of degraded RNA, and proteins of approximately 76,000 and 45, 000 daltons. The 76,000-dalton proteins from intracisternal A and extracellular particles have the same cyanogen bromide peptides. Hybridization kinetic analysis indicates that the RNAs in the two particles are identical or very closely related and share partial homology with Moloney leukemia virus RNA. In contrast, the particles appear to have little or no relationship to murine mammary tumor virus as judged by several different criteria. Electron microscope studies indicate that the extracellular particles arise from the budding of core components through the plasma membrane. These results suggest that the intracisternal A and extracellular oncornavirus-like particles produced by MOPC-460 cells are closely related.

Animals↗
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↗
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↗