TRANSCRIPTION OF A REPRESSED GENE: EVIDENCE THAT IT REQUIRES DNA REPLICATION

It is known that the synthesis of DNA is not essential for constitutive or induced enzyme synthesis. Our studies indicate that DNA synthesis is required for the basal level synthesis (that is, for synthesis in absence of inducer) of two inducible enzymes, a finding which supports an earlier speculation that a messenger-RNA transcription event may normally accompany DNA replication. Studies with cultures of Escherichia coli TAU-bar in which DNA replication is synchronized suggest that the beta-galactosidase gene is transcribed at a particular time in the sequential replication of the bacterial chromosome.

IONIZING RADIATION: EFFECT ON GENETIC TRANSCRIPTION

Cells of Escherichia coli grown on maltose can be induced by the addition of thiomethyl galactoside to produce beta-galactosidase. If cells are irradiated shortly after induction, the transcription of the DNA ceases, and the enzyme produced by the messenger RNA is observed to reach a maximum. From these data the calculated half-life of unstable messenger RNA is given over a temperature range from 8.1 minutes at 10 degrees C to 0.7 minute at 45 degrees C. The kinetics of cessation of transcription give information on both meassenger RNA decay and rate of transcription. Arrhenius graphs for both these rates are given, and the activation energies mtieasured are 11,000 calories per mole for decay and 22,000 calories per mole for transcription. This relation to temperature is characteristic of enzymatic behavior.

CONSERVATION OF RIBOSOMAL AND MESSENGER RIBONUCLEIC ACID CISTRONS IN BACILLUS SPECIES

Doi, Roy H. (Syracuse University, Syracuse, N.Y.), and Richard T. Igarashi. Conservation of ribosomal and messenger ribonucleic acid cistrons in Bacillus species. J. Bacteriol. 90:384-390. 1965.-Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) fractions from various Bacillus species were tested for interspecies DNA-RNA hybrid formation. DNA preparations from B. subtilis, B. cereus, B. megaterium, B. stearothermophilus, and B. macerans, whose base composition varied from 33 to 50% guanylate + cytidylate content, were used in the hybrid annealing mixtures with pulse-labeled RNA from sporulating cells and from log-phase cells of B. subtilis and B. cereus. Efficient hybridization in these cases was obtained only in homologous annealing situations. When heterologous DNA and RNA preparations were tested for hybrid formation, only 1 to 6% of the homologous hybridization was obtained. Although the efficiency of hybrid formation was low, the results were reproducible. No difference in efficiency of hybrid formation was observed between the messenger RNA from sporulating cells and that from log-phase cells. When B. subtilis ribosomal RNA was placed in annealing mixtures with heterologous DNA, 47.5 to 62.9% of the homologous hybridization was obtained. These results suggest that a small number of identical sequences are present among the Bacillus species. Furthermore, the ribosomal RNA cistrons appear to be more highly conserved relative to other genetic sequences.

BIPOLARITY OF INFORMATION TRANSFER FROM THE SALMONELLA TYPHIMURIUM CHROMOSOME

Apparently the leucine and tryptophan gene clusters are polarized in opposite directions on the Salmonella chromosome. Either the direction of polarity is independently determined for each operon or the bacterial chromosome may consist of more than one multi-operon unit of DNA, each such unit determining the direction of polarity of its constituent genes. Each hypothesis results in a different prediction concerning the distribution of operon polarity directions on the chromosome and the functional status of chromosomal inversions.

THE BIOSYNTHESIS OF ALKALINE PHOSPHATASE WITH A PARTICULATE FRACTION OF ESCHERICHIA COLI

1. By digitonin lysis of penicillin spheroplasts of Escherichia coli a particulate fraction P(1) was previously obtained that supported the sustained synthesis of alkaline phosphatase when supplied with amino acids, nucleotide triphosphates and other cofactors. This P(1) fraction, when subjected to mild ultrasonic treatment in the presence of sucrose and Mg(2+), yielded the P(1)(S) fraction, consisting of integrated particulate subcellular particles containing DNA and RNA. 2. The P(1)(S) fraction from E. coli K10 wild type (R(+) (1)R(+) (2)P(+)) grown under repressed conditions supported the immediate synthesis of alkaline phosphatase in vitro. The synthesis occurred in phases. The first was followed by a lag, and then there was a linear rapid phase that continued for at least 3hr. Actinomycin D inhibited the appearance of the second phase. It was concluded that the particles are programmed to synthesize enzyme even when prepared from repressed cells, and therefore that synthesis of the specific messenger RNA for alkaline phosphatase in vivo was not inhibited when the bacteria were grown in an excess of inorganic phosphate. 3. Phosphate inhibited synthesis of enzyme to the same extent with the P(1)(S) fractions of two constitutive strains as with the P(1)(S) fraction of the wild-type strain. 4. Inorganic phosphate inhibited amino acid incorporation with the P(1)(S) fraction and also inhibited enzyme synthesis in vitro. The effect on amino acid incorporation could be partially overcome by adding Mn(2+) to the incubation mixtures. However, Mn(2+) inhibited the synthesis of alkaline phosphatase. Also, inhibition of the incorporation of [(32)P]CTP into RNA was overcome by Mn(2+). The effect of phosphate on amino acid uptake was most probably due to a phosphorolysis of RNA by polynucleotide phosphorylase, also present in the P(1)(S) fraction. This phosphorolysis may be responsible for the instability of messenger RNA in vitro and in vivo. 5. Phosphate also specifically inhibited the formation of alkaline phosphatase, since it did not affect markedly the induced formation of beta-galactosidase by the same P(1)(S) fraction. The specific effect is attributed to the prevention of formation of the enzymically active dimer from precursors, a Zn(2+)-dependent reaction. It is suggested that the repression of the synthesis of alkaline phosphatase in vivo in the wild-type strain was the sum of these two effects.

INHIBITION OF PROTEIN SYNTHESIS IN MAMMALIAN CELL-FREE SYSTEMS BY CHLORAMPHENICOL

Chloramphenicol can inhibit protein synthesis in mammalian cell-free systems as effectively as it inhibits protein synthesis in analogous microbial systems. Significant inhibition in mammalian systems was obtained only when protein synthesis was stimulated by the addition of template RNA to the system, there being comparatively little inhibition of protein synthesis by ribosomes in the absence of stimulatory RNA. It is postulated that chloramphenicol may inhibit the function of messenger or template RNA by successfully competing for ribosomal binding sites, thereby preventing the attachment of RNA to ribosomes. The apparent discrepancy in the sensitivity of mammalian and microbial cells to chloramphenicol may be related to differences in turnover or stability of ribosomal template RNA rather than to intrinsic differences in mechanism of protein synthesis. These observations are in accord with the suggestion that protein synthesis in intact mammalian cells may be susceptible to chloramphenicol inhibition only at the time that new messenger or template RNA is being deposited on ribosomes and that more mature cells may be resistant because informative RNA already deposited on ribosomes is not accessible to chloramphenicol inhibition. The inhibitory effect of chloramphenicol on protein synthesis in proliferating cells may be an important factor in hematologic toxicity attributable to chloramphenicol.

HISTONE PROTEIN TRANSITION IN DROSOPHILA MELANOGASTER. II. CHANGES DURING EARLY EMBRYONIC DEVELOPMENT

Employing cytochemical methods it was found that during the early embryonic development of Drosophila melanogaster the nuclei contain in sequence two kinds of chromosomal proteins. The cleavage nuclei (as also the pronuclei), until shortly before the blastoderm stage, contain an atypical (or juvenile) histone, stainable with bromophenol blue but not with alkaline fast green. The typical fast green-positive histone appears at the close of the period of the synchronized cleavage mitoses, just before blastulation, when nucleoli are first produced. The amount of DNA of the cleavage nuclei, as determined cytophotometrically, is nearly constant; therefore, the DNA moiety of the nucleohistone complex seems to remain unaffected by the protein shift during embryonic development. The implications of the protein shift in relation to the histone control of gene expression are discussed.

LONG-LIVED MESSENGER RNA: EVIDENCE FROM COTTON SEED GERMINATION

In germinating cotton embryos the partial inhibition of RNA synthesis by actinomycin D does not inhibit the incorporation of leucine-(14)C into soluble protein nor cause a loss of polyribosomes during the first 16 hours of germination. This suggests that the protein synthesis observed during this period is directed by messenger RNA which exists in the mature seed and which is not rapidly degraded and resynthesized.

EXTRACELLULAR RIBONUCLEASE FORMATION IN BACILLUS SUBTILIS AND ITS STIMULATION BY ACTINOMYCIN D

1. Extracellular ribonuclease is produced linearly for at least 3hr. by washed post-logarithmic-phase cells of Bacillus subtilis suspended in a medium containing maltose (1%) and casein hydrolysate (0.5%). 2. Low concentrations of actinomycin D (less than 2mug./ml.) stimulate ribonuclease formation, the maximum effect being observed with a concentration of 1mug./ml. Concentrations greater than 2mug./ml. are inhibitory. There is no parallel stimulation of alpha-amylase formed under the same conditions, and [(14)C]uracil incorporation into a perchloric acid-insoluble form is inhibited. 3. The actinomycin D-induced stimulation is not due to the presence of an activator, nor is the inhibition due to the release of an inhibitor by the cells. The effect is on the amount of ribonuclease produced in the medium. 4. Extracellular ribonuclease formation is partially inhibited by anaerobiosis, 2,4-dinitrophenol, sodium azide and by chloramphenicol and puromycin. 5. High concentrations of antibiotic do not completely inhibit ribonuclease formation, but a basal amount of enzyme representing 20min. synthesis in an uninhibited system is always produced. This ;antibiotic-insensitive' enzyme could possibly represent preformed enzyme ;in the pipe-line' en route to secretion. 6. The stimulated appearance of ribonuclease in the presence of 1mug. of actinomycin D/ml. is shown to be dependent on enzyme synthesis. The mechanism of this effect is discussed.

THE SEQUENTIAL SYNTHESIS OF THE POLYPEPTIDE CHAIN OF SERUM ALBUMIN BY THE MICROSOME FRACTION OF RAT LIVER

1. The isolated microsome fraction of regenerating rat liver was incubated with cell sap, a source of energy and [(35)S]methionine, [(14)C]isoleucine or [(14)C]leucine for different periods of time, and microsomal albumin isolated. 2. The distribution of these isotopes in albumin was determined by separation of tryptic peptides from the protein. Radioactivity was measured in peptides either qualitatively by radioautography or quantitatively by labelling with both (3)H and (14)C. 3. A gradient of radioactivity existed at all times in albumin isolated after incubating microsomes. 4. The shorter the incubation time the fewer the peptides labelled in albumin, but the peptides with highest specific activity after short incubation times corresponded to those with highest specific activities after long incubation times. 5. Leucine released from the C-terminus of albumin had a higher specific activity than the mean specific activity of the remaining leucine residues in albumin. 6. The peptide with the highest specific activity in albumin is probably derived from the C-terminus of the protein. 7. [(14)C]Glutamic acid is incorporated into the N-terminus of albumin after incubating the microsome fraction with this isotopically labelled amino acid, cell sap and a source of energy. The specific activity of the N-terminal glutamic acid under these conditions is less than the mean specific activity of the remaining glutamic acid and glutamine residues in albumin. 8. The results are interpreted as reflecting a sequential synthesis of serum albumin in the isolated microsome fraction of rat liver. The direction of synthesis of albumin is from the N-terminus towards the C-terminus. 9. The bulk of incorporation of radioactive amino acid into albumin in the isolated microsome fraction is due to completion of partially completed, pre-existing peptide and polypeptide chains. A limited synthesis of new chains of albumin does, however, occur.