Biochimica et Biophysica Acta (BBA) - Specialized Section on Nucleic Acids and Related Subjects最新文献

• 1.

  1. A deoxyribonucleoprotein, found in extracts of Escherichia coli B(H), has been investigated with respect to its role in DNA and RNA synthesis.

• 2.

  2. A deoxyribonucleoprotein in ribosome-free cell extract could be separated from the other cellular components either with gel filtration or zone electrophoresis.

• 3.

  3. The isolated deoxyribonucleoprotein was composed of roughly 80% of DNA a and 20% of protein.

• 4.

  4. Association of DNA polymerase (deoxynucleosidetriphosphate: DNA deoxynucleotidyltransferase, EC 2.7.7.7) and RNA polymerase (nucleosidetriphosphate: RNA nucleotidyltransferase (DNA dependent), EC 2.7.7.6) with this deoxyribonucleoprotein has been demonstrated.

• 5.

  5. DNA polymerase and RNA polymerase, purified from E. coli extract, had an ability to form a complex with DNA.

Yeast RNA has been examined, using moving-boundary electrophoretic procedures, in several buffer systems covering the pH interval 3–10 and the ionic strength range 0.025–0.5. The studies suggest that the purity of RNA is better evaluated at pH 3 and pH 10 than in the intermediate pH range. In buffers containing phosphate or cacodylate ions, lack of enantiography between patterns from ascending and descending limbs of the cell indicate RNA-buffer interactions. The mobility of RNA at the same ionic strength −10.1·10⁻⁵ cm² V⁻¹ sec⁻¹ at pH 3 is 72% of the mobility, −14.0·10⁻⁵ cm² V⁻¹ sec⁻¹ found at pH 10.

The administration in vivo of 3-methylcholanthrene (MC) increases the rate of leucine incorporation in a nuclei-free rat-liver homogenate system. Each subcellular fraction, the mitochondria, microsomes and supernatant fluid contribute to the increased activity in the MC preparation. The major part of the incorporation takes place in the microsomal fraction. The increase in incorporation in the microsomes from MC-treated rats is not secondary to changes in the concentration of magnesium ion or GTP. Parallel changes in the activity of the supernatant fluid appear due to a more adequate maintenance of proper GTP levels in the supernatant from MC-treated rats.

The interrelationships between the free and bound ribosomes of the hepatic cell in the regenerating rat liver have been studied by an examination of the metabolic relationships between RNA's of these two kinds of particles.

The kinetics of incorporation of [¹⁴C]orotic acid show no precursor-product relationship between the RNA's of free and bound ribosomes. This means that there is no systematic derivation of one kind of particle from the other. So, it is not obligatory for the life of a newly synthesized ribosome to proceed from that of a free state to that of a membrane-bound state, or inversely.

The results do not establish, however, that the two populations are independent. Indeed, the kinetics suggest the possibility of a constant exchange between them.

In addition, a precursor-product relationship has been found between nuclear RNA and ribosomal RNA. The different results are discussed.

• 1.

  1. The inhibitory effect of extracts of rat liver on DNA polymerase (deoxyribonucleosidetriphosphate: DNA deoxyribonucleotidyltransferase, EC 2.7.7.7) has been investigated.

• 2.

  2. Fractionation of the crude extracts has revealed that the inhibition is not due to the hydrolysis of the deoxyribonucleoside 5′-triphosphates by phosphatases.

• 3.

  3. The inhibitory factor was purified about 10–15-fold, with a yield of 20%.

• 4.

  4. Its activity was due to the action on the primer DNA of a deoxyribonuclease, and the oligonucleotide products of the reaction inhibited the polymerase.

• 5.

  5. The properties of the deoxyribonuclease differed in some respects from those of splenic deoxyribonuclease II (deoxyribonucleate 3′-nucleotidohydrolase, EC 3.1.4.6) and pancreatic deoxyribonuclease I (deoxyribonucleate oligonucleotidohydrolase, EC 3.1.4.5). In particular, it hydrolyses thermally denatured DNA more rapidly than native DNA.

• 1.

  1. A procedure for preparing rat-liver mitochondria including a pre-incubation with RNAase (EC 2.7.7.16) to inactivate the microsomal system for amino acid incorporation is described.

• 2.

  2. The inhibition of the incorporation of amino acids into mitochondrial protein by adding substrate is correlated with a lowering of the NADP⁺/NADPH ratio.

• 3.

  3. It is shown that ammonia can relieve the inhibition by α-oxoglutarate or isocitrate of the incorporation into liver mitochondria, that this effect is not due to the glutamate formed, and that this is correlated with oxidation of NADPH to NADP⁺.

• 4.

  4. The role of endogenous substrate is discussed. It is concluded that in the case of rat-liver mitochondria α-oxoglutarate plus ammonia give the best conditions for providing energy for incorporation, since a high NADP⁺/NADPH ratio is also assured.

• 5.

  5. Judged by the effects of oligomycin and 2,4-dinitrophenol on the amino acid incorporation into protein by mitochondria, the possibility is discussed whether and in how far the high-energy intermediates of oxidative phosphorylation can meet the energy requirements for the incorporation process.