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

A simple method for the separation and partial purification of aminoacyl-RNA synthetases (aminoacid-RNA ligases, EC class 6.1.1) specific for tryptophan, tyrosine, methionine, isoleucine, cysteine, valine and leucine from Escherichia coli is described. The separations are achieved by chromatography of particle-free bacterial extracts on substituted polysaccharide resins.

• 1.

  1. When Ehrlich ascites cells are incubated in the presence of glucose, uridine, or cytidine, the intracellular concentration of free glutamate is greatly increased. The specific activity of [¹⁴C]glutamate formed from [¹⁴C]glucose is decreased 50% in the presence of 1 mM uridine.

• 2.

  2. [¹⁴C]Formate incorporation into both proteins and nucleic acids of Ehrlich ascites cells is greatly stimulated by glucose, uridine, glutamine and glutamate.

• 3.

  3. Methionine sulphoximine completely prevents the stimulations of formate utilization by glucose and uridine. These effects of methionine sulphoximine are reversed by glutamine.

• 4.

  4. It is suggested that the increased intracellular concentration of glutamate in the presence of exogenous glucose, uridine or glutamate leads to an increased availability of glutamine necessary for the synthesis of purine nucleotides and proteins. The availability of glutamate appears to be limiting for amino acid incorporation into proteins.

• 5.

  5. Exogenous [¹⁴C]glutamate is very poorly transported by Ehrlich ascites cells. After 1 h of incubation, a ratio of 0.3 for the distribution of radioactivity between cells and medium is obtained.

• 6.

  6. The incorporation of [¹⁴C]formate into free serine is stimulated 20–40-fold by glucose, uridine and cytidine. [¹⁴C]Formate incorporation into serine is greater under anaerobic conditions than under aerobic conditions.

• 1.

  1. The nucleotide composition and nucleotide arrangement of soluble RNA in the posterior silkgland have been compared for two kinds of silkworm, which produce two different kinds of fibroin which differ in their amino acid composition.

• 2.

  2. The s-RNA's from the two kinds of worm are similar to each other in their nucleotide composition and arrangement.

• 3.

  3. Some differences have been observed in the nucleotide arrangements when compared with yeast s-RNA. A few minor components including pseudo-uridylic acid are also detected in silkgland s-RNA.

• 4.

  4. The composition of the ribosomal RNA is similar in the two kinds of worm.

Enzymic hydrolysis of ultraviolet-irradiated DNA with venom phosphodiesterase (EC 3.1.4.1) yields oligonucleotide sequences that are resistant to enzymic degradation. Most of the oligonucleotides contain thymine dimers in sequences whose general structure is pXp$\text{TpT}$. The number and type of the dimer-containing trinucleotides depend on the base composition of the DNA, the irradiating wavelength, and the incident dose. Dimers in native DNA are eliminated by treatment of the DNA with an extract from yeast in the presence of 360-mμ light. They are eliminated very slowly from denatured DNA and not at all from trinucleotides. The splitting of dimers in trinucleotides by 240-mμ irradiation is independent of the base X in pXp$\text{TpT}$, but the rate of formation of dimers by 280 mμ depends on the third base.

• 1.

  1. Developmental changes in total pancreatic protein, DNA, RNA and α-amylase (α-1,4-glucan 4-glucanohydrolase, EC 3.2.1.1) activity were studied in chick embryos aged 10–20 days and in 1–5-day-old chicks (developmental age 21–25 days).

• 2.

  2. The protein content of the pancreas increases rapidly from 10 to 13 days, more slowly from 13 to 18 days, very rapidly from 19 to 22 days and again more slowly from 22 to 25 days.

• 3.

  3. A virtually constant concentration of RNA per mg of protein is observed from 13 to 25 days of development. On the other hand, the concentration of DNA per mg of protein, which is constant from 13 to 18 days, falls sharply between 18 and 21 days.

• 4.

  4. The specific activity of amylase remains constant from 11 to 16 days of development and increases about 8-fold from 16 to 22 days, after which it falls. At its maximum concentration (22–23 days) amylase constitutes about 12% of the total pancreatic protein.

• 5.

  5. It seems significant that the steepest rise in amylase activity between 18 and 22 days coincides with the period of rapid growth and increase in cell size which overlaps the time of hatching.

In order to obtain more information on the specificity of micrococcal nuclease (EC 3.1.4.7), three series of substances were investigated:

• 1.

  1. The series of polypyrimidine nucleotides terminated at both ends by phosphoryl groups obtained by controlled hydrolysis of DNA.

• 2.

  2. Polythymidylic acids obtained by chemical synthesis.

• 3.

  3. Three naturally occuring deoxyribonucleic acids.

Using catalytic amounts of highly purified enzyme, it was shown that tri- and tetranucleotides are attacked with the liberation of the 3′-terminal nucleoside and (or) nucleotide in a stepwise manner. With pentanucleotides, exonucleolytic and endonucleolytic mechanisms of hydrolysis occur at the same rate. The fact that the enzyme attacks preferentially thymine and adenine linkages has been confirmed by using deoxyribonucleic acids containing different adenine-thymine ratios.