Rate Of Nucleic Acid Synthesis Research Articles

Magnesium starvation of Aerobacter aerogenes. II. Rates of nucleic acid synthesis and methods for their measurement.

The rates of synthesis of Aerobacter aerogenes nucleic acids were estimated during incubation of the bacteria in a Mg(++)-free medium. Deoxyribonucleic acid (DNA) synthesized during Mg(++) starvation, or in the preceding exponential growth, remained acid-precipitable for 2.5 hr before breaking down to acid-soluble products during a period of many hours. Rates of DNA synthesis were calculated by correcting the net amounts of DNA per milliliter to values that would have appeared had there been no decay. After the first few hours, this rate was constant, the amount of DNA present at the start of Mg(++) starvation being synthesized every 130 min. Rates of synthesis of total ribonucleic acid (RNA) were established in two ways: (i) by measurements of the incorporation of exogeneous uracil and glucose carbon into RNA, and (ii) by the accumulation of transfer RNA (tRNA), since this component is stable during Mg(++) starvation. After the first few hours, this rate was constant, the amount of RNA present at the start of Mg(++) starvation being synthesized about every 120 min. Fractionation by gradient centrifugation revealed that at all times of starvation the ratio of newly synthesized tRNA-rRNA was the same as it was during exponential growth. Furthermore, newly synthesized ribosomal RNA (rRNA) became a part of polysomal structures. Thus, in the absence of Mg(++), DNA, tRNA, and rRNA were synthesized in the same relative proportions as during exponential growth, at rates close to one-half the instantaneous rates of synthesis in the bacteria growing exponentially at the start of starvation.

Nucleic acid synthesis in various tissues of the rat. During rejection of skin homografts.

THE PRIMARY SITE of the host response in the case of skin homografts has been identified as the regional lymph nodes draining the graft. This has been demonstrated by a variety of techniques: passive transfer of immunity, 1 gross weight, 2 and histologic response. 2,3 Similar experiments have indicated that the spleen is also a site for this response. 1,3,4 Although the techniques employed in these experiments have provided valuable qualitative information about the host response, none, alone or in combination with each other, provides quantitative data about the host response. All of these techniques measure the amount of response in a tissue at a given time, and yet fail to measure the rate of response of the tissue. In the present experiments the rate of nucleic acid synthesis has been utilized as a measure of the rate of tissue response while the whole organ weight has been employed

Turnover of protein and nucleic acid in soluble and ribosome fractions of non-growing Escherichia coli

The stability of protein and of RNA has been examined in the ribosome and soluble fractions of non-growing E. coli. In both fractions there is balanced degradation and re-synthesis of protein at about 5% per h. The RNA of the ribosomes is also degraded at this rate but re-synthesized at only 1.5% per h. In the soluble fraction the rate of nucleic acid synthesis exceeds the rate of degradation, so that there appears to be net transfer of material from the ribosomes to the soluble fraction. Degradation of ribosomes supplies much of the free amino acids and almost all of the ribonucleotides passing through the free pool during starvation.

Effect of vitamin B12 on nucleic acid metabolism of the rat.

Summary1. The amounts of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in the livers of rats fed a vit. B12 deficient diet were significantly lower per g of fresh or of dry liver or of liver nitrogen than those for the supplemented rats. No difference was observed, however, in the amounts of RNA and DNA per cell for the deficient or supplemented rats. The amount of nucleic acids per g of spleen or kidney was the same Spherule Antigen and Complement Fixation for the deficient and supplemented group. 2. Other studies indicated that the rates of incorporation of N15 glycine into the purines of RNA were lower for the deficient animals. 3. These studies suggest that in a vit. B12 deficiency the reduced rate of nucleic acid synthesis in the liver reduced the rate of cell divisions.