Initiation and termination of bacterial deoxyribonucleic acid replication in low concentrations of chloramphenicol

recF and recR are required for the resumption of replication at DNA replication forks in Escherichia coli

Escherichia coli containing a mutation in recF are hypersensitive to UV. However, they exhibit normal levels of conjugational or transductional recombination unless the major pathway (recBC) is defective. This implies that the UV sensitivity of recF mutants is not due to a defect in recombination such as occurs during conjugation or transduction. Here, we show that when replication is disrupted, at least two genes in the recF pathway, recF and recR, are required for the resumption of replication at DNA replication forks, and that in their absence, localized degradation occurs at the replication forks. Our observations support a model in which recF and recR are required to reassemble a replication holoenzyme at the site of a DNA replication fork. These results, when taken together with previous literature, suggest that the UV hypersensitivity of recF cells is due to an inability to resume replication at disrupted replication forks rather than to a defect in recombination. Current biochemical and genetic data on the conditions under which recF-mediated recombination occurs suggest that the recombinational intermediate also may mimic the structure of a disrupted replication fork.

Regulation of DNA synthesis and capacity for initiation in DNA temperature sensitive mutants of Escherichia coli I. Reinitiation and chain elongation

The capacity for initiation and subsequent chain elongation was examined in several DNA temperature sensitive mutants of Escherichia coli after the mutants had been held at nonpermissive temperature for approximately 1.5 generation equivalents and then returned to permissive temperature in the presence of chloramphenicol. The results obtained indicate that 4-5 sets of replication forks can be initiated after return to permissive temperature in the presence of chloramphenicol but the forks apparently become stalled and fail to complete chromosomal replication in the presence of chloramphenicol. In temperature reversible dnaA mutants, once the chloramphenicol is removed the forks appear to be able to resume replication at the nonpermissive temperature. The relationship between premature initiation and premature chain termination is discussed.

Effect of blocking protein synthesis at nonpermissive temperatures on temperature-sensitive deoxyribonucleic acid mutants of Escherichia coli

When protein synthesis was blocked in temperature-sensitive deoxyribonucleic acid synthesis mutants of Escherichia coli at nonpermissive temperatures, it reduced the amount of apparent subsequent chain elongation to approximately half that observed in the mutants either at nonpermissive temperatures alone or when protein synthesis was blocked at the permissive temperature. Blocking protein synthesis at the nonpermissive temperatures for periods of 40 min caused the loss of ability to reinitiate deoxyribonucleic acid synthesis at the permissive temperature.

Replication of DNA in UV-irradiated Escherichia coli in the absence of amino acids

Since pyrimidine dimers are considered to be the cause of the synthesis of short DNA segments, normalization of DNA replication after UV irradiation should be in a temporal correlation with their removal. This correlation holds in exponentially growing excision-proficient Escherichia coli cells. However, when these cells are preincubated and postincubated without amino acids, synthesis of short segments continues although dimers are efficiently excised.

Deoxyribonucleic acid synthesis after inhibition of initiation of rounds of replication in Escherichia coli B/r

The theory describing the effect of inhibition of initiation of rounds of deoxyribonucleic acid (DNA) replication on the accumulation of DNA is derived, and an analysis is presented which allows the determination of the time C taken to replicate the bacterial chromosome from the kinetic changes in the accumulation of DNA. This analysis is applied to experiments in which inhibition of initiation was achieved by inhibiting protein or protein and ribonucleic acid synthesis with chloramphenicol or rifampin. The results for both antibiotics are identical and indicate that there is a delay of 6 to 11 min in the effect of the antibiotics on initiation of rounds of replication. If this delay is taken into account, then the value of the C period estimated from such experiments agrees with values obtained by other methods, whereas by conventional data evaluation of such experiments the C period would be overestimated. In the low thymine-requiring derivative of Escherichia coli B/r ATCC 12407 used here, the C period was found to be between 38 and 41 min for cultures growing with a mass doubling time of 29 min in glucose-amino acids medium, supplemented with 20 micrograms of thymine/ml.

Tetracycline inhibits propagation of deoxyribonucleic acid replication and alters membrane properties

Tetracycline, at concentrations greater than required for inhibition of protein synthesis, rapidly and completely inhibits replication of deoxyribonucleic acid (DNA) in Escherichia coli and Bacillus subtilis. At these concentrations of tetracycline, synthesis of ribonucleic acid is not appreciably altered. In addition to inhibiting DNA replication, tetracycline causes alterations of the cytoplasmic membrane resulting in leakage of intracellular pools of nucleotides, amino acids, and the non-metabolizable sugar analogue, thiomethylgalactoside. As DNA is synthesized at a site on the membrane, alterations of membrane structure by tetracycline may be responsible for the observed inhibition of DNA replication.

Nuclear and cell division in Bacillus subtilis. Antibiotic-induced morphological changes

Incubation of Bacillus subtilis after outgrowth from spores in the presence of four different antibiotics in two different concentrations, showed that septation can occur without termination of nuclear division. Septation is then only partially uncoupled from the normal division cycle. Observations on location and development of mesosomes in the presence of the antibiotics, made in three-dimensional cell reconstructions, suggest that the mesosome plays a role in the normal coordination between nuclear and cell division, and may explain the partial independence between these two processes in B. subtilis.

Differential sensitivity to antibiotics of trp mRNA synthesis originating at the trp promoter and the lambda promoter

Transcription of the Escherichia coli trp operon translocated into the early region of bacteriophage lambda can occur under the control of either of two promoters, the trp promoter on the lambda promoter (OL of N gene). (Imamato, F. and Tani, S. (1972) Nat. New Biol. 240, 172-175 and Ihara S. and Imamoto, F. (1976) Biochim. Biophys. Acta 432, 199-211). Trp mRNA synthesis originating at the trp promoter stopped when translation was blocked by chloramphenicol tetracycline erythromycin or puromycin. In contrast, trp mRNA synthesis originating at the lambda promoter was not affected by antibiotic action. This probably is a reflection of the properties of the "immediate early" class of genes of lambda, whose transcription in initiated at the PL. promoter and is not inhibited by the antibiotic. The inference is strengthened by comparable results with phage lambdatrpE-A (carrying an intact tro operon) and lambdatrpBA (carrying the operator-distal two genes but missing the trp promoter and operator). Thus it seems that either the promoter or other gene(s) located at the beginning of the operon, either at polymerase addition or because of some feature of the transcript, can determine a requirement for "coupling" of RNA polymerase to the translational machinery in vivo.

Direction of deoxyribonucleic acid replication in Escherichia coli under various conditions of cell growth

The direction of chromosome replication in a temperature-sensitive initiation mutant of Escherichia coli (CT28) is shown autoradiographically to be bidirectional. This mode of replication persists even when the rate of replication is reduced by slow growth in succinate minimal medium or in the presence of chloramphenicol. Therefore, although the rate of replication can be affected by certain physiological stimuli, the topology of replication need not be.

Alterations of the rate of movement of deoxyribonucleic acid replication forks

Antibiotics that inhibit ribonucleic acid (RNA) or protein synthesis are often used in studies of deoxyribonucleic acid (DNA) synthesis. The experiments presented here demonstrate that the rate of movement of DNA replication forks can be influenced by such antibotics. Addition of either chloramphenicol, which inhibits movement of ribosomes along messenger RNA, or streptolydigin, which inhibits movement of RNA polymerase, leads to a decrease in the rate of fork movement. Rifampin, which inhibits initiation of RNA synthesis, reverses the effects of chloramphenicol or streptolydigin. The slowed movement of DNA replication forks is discussed in terms of obstruction of fork movement by transcription complexes temporarily immobilized on the DNA template.

Accumulation of the capacity of initiation of deoxyribonucleic acid replication in Escherichia coli

Several temperature-sensitive initiation mutants of Escherichia coli were examined for the ability to initiate more than one round of replication after being held at nonpermissive temperature for approximately 1.5 generation equivalents. The capacity for initiation was measured by residual synthesis experiments and rate experiments under conditions where protein synthesis and ribonucleic acid synthesis were inhibited. Results of the rate and density transfer experiments suggest that the cells may initiate more than one round of replication in the absence of protein or ribonucleic acid synthesis. This contrasts with the results of the residual synthesis experiments which suggest that, under these conditions, only one round of synthesis is achieved. These findings suggest that the total amount of residual synthesis achieved in the presence of an inhibitor may be both a function of the number of initiation events which occur and the effect of the inhibitor of protein or ribonucleic acid synthesis on chain elongation.

Polypeptide formation and polyribosomes in Escherichia coli treated with chloramphenicol

In Escherichia coli cultures maximally inhibited with chloramphenicol, formation of polypeptides still continued at a slow, constant rate for at least 90 min. The rate of leucine incorporation was reduced to 0.5%, but methionine was only reduced to 2%, suggesting that chains are normally initiated with methionine but are prematurely released at a short chain length. Consistent with this possibility was the distribution of the products on Sephadex columns: a range of peptides longer than 4 and shorter than 60 to 70 residues was seen. Less than 10% of the peptides broke down during a chase with cold amino acids, and during continuous labeling they accumulated progressively. On the average, one peptide was formed per ribosome every 5 min. Peptide synthesis in the presence of chloramphenicol was still dependent on ribosome translocation; it stopped in a mutant with an inactivated temperature-sensitive elongation factor G. But even in the absence of translocation, new messenger ribonucleic acid (mRNA) chains were found joined to one or a few ribosomes. The chains had a size distribution comparable to that of mRNA from polyribosomes of growing cells. They were stabilized for an average time of about 5 min, but were more rapidly degraded after puromycin was added to the cells. This suggests that stabilization may be related to the average time spent by a ribosome on an mRNA chain, with or without polypeptide formation.

Replication of bacteriophage phiX174 DNA in a temperature-sensitive dnaC mutant of escherichia coli C

Bacteriophage phiX174 cannot grow in a temperature-sensitive dnaC mutant of Escherichia coli C at the nonpermissive temperature. The inability to grow is the result of inhibition of virus DNA synthesis. Parental replicative form synthesis is not temperature sensitive. Single-stranded virus DNA continues to be synthesized for at least 45 min after shifting to the nonpermissive temperature late in infection. In contrast, the replication of the replicative form terminates within 5 min after shifting to the nonpermissive temperature.