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M M Nass

Publications and source records attributed to M M Nass.

42 records · Page 3Linked to original sources
PubMed1969

Comparative hybridization of mitochondrial and cytoplasmic aminoacyl transfer RNA with mitochondrial DNA from rat liver.

We have tested the specificity of hybridization of mitochondrial tRNA with mitochondrial DNA. Techniques are now available for performing RNA-DNA hybridization at low temperatures in the presence of 50 per cent formamide. With this technique, specific aminoacyl-tRNA-DNA hybridization can be followed in the presence of other species of RNA if the tRNA is acylated with radioactive amino acids. With this technique, mitochondrial leucyl-tRNA from rat liver has been found to anneal to mitochondrial DNA. Competitive hybridization between mitochondrial leucyl-tRNA and mitochondrial or cytoplasmic aminoacyl-tRNA shows that mitochondrial tRNA competes much more efficiently than cytoplasmic tRNA for sites of annealing to mitochondrial DNA. These results show that mitochondrial leucyl-tRNA differs from cytoplasmic leucyl-tRNA in its primary base sequence. They also imply that mitochondrial DNA may be the template from which mitochondrial tRNA is transcribed.

Amino Acids↗
PubMed1968

T6r+-induced proteins and nucleic acids in Escherichia coli infected in the presence of streptomycin.

Streptomycin does not strongly inhibit T-even phage multiplication in the streptomycin-susceptible polyauxotroph, Escherichia coli strain T(-)H(-)U(-). The relatively slight inhibition, observed earlier, on production of late proteins has now been studied further. The phage-induced ribonucleic acid, synthesized in T6 phage infection in the presence of streptomycin, has been characterized by its base composition, size distribution, and behavior in hybridization tests. Comparison of these properties to those of control samples, taken during either early or late periods of infection, have not shown any significant differences. Phage-induced proteins, synthesized at different times during infection, were studied by disc-gel electrophoresis. Staining and autoradiography of the patterns of pulse-labeled proteins, formed in the absence and presence of the antibiotic showed only slight quantitative changes in the appearance of early proteins. More marked quantitative effects were detected later in infection. Nevertheless, changes in the mobilities of the different proteins were not observed in the streptomycin-treated cultures at any time after infection, suggesting the absence of gross misreading sufficiently great to alter the distinctive electrophoretic patterns of the extracts. Cells infected and incubated in the presence of the antibiotic were found to contain intact virus particles, as shown by electron microscopy. Such infected cells contained extensive deoxyribonucleic acid pools and did not develop the rounded nucleoids with enclosed dense bodies characteristic of the lethal action of the antibiotic. On the other hand, infected bacteria previously exposed to lethal concentrations of streptomycin were unable to synthesize the early enzymes, deoxycytidylate (dCMP) hydroxymethylase and dihydrofolate reductase, or to make phage deoxyribonucleic acid and phage. Such previously killed cells contained the rounded and clotted nucleoids and were unable to unravel this pathological structure after phage infection.

Autoradiography↗