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At least 19 recordsLinked to original sources
PubMed2026

DNA polymerase I: structure, activity, and function in bacterial DNA replication and repair.

Faithful replication and repair of the genome are essential processes for all life. Genome maintenance is coordinated by a complex suite of proteins, with bacteria evolving intricate systems despite their relatively simplistic genomes. DNA polymerases are a key class of proteins that mediate genome maintenance. DNA polymerases are all capable of extending nascent strands of DNA but contribute to DNA replication and repair in distinct ways depending on their active site and substrate specificity. The first discovered polymerase, bacterial DNA polymerase I (Pol I), has long been considered the primary enzyme responsible for Okazaki fragment maturation and resynthesis in many DNA repair pathways. These conclusions derive primarily from studies using the gram-negative bacterium, Escherichia coli. Given that some bacterial lineages diverged from E. coli over a billion years ago, these assumptions may not account for evolution in functional diversity. In this review, we examine the structural features of bacterial Pol I and discuss how each of its distinct enzymatic activities contribute to genome maintenance. Throughout, we introduce differences that have been discovered between gram-negative and gram-positive species and explore how activity differences may translate to functional adaptations in replication or repair. We focus on evidence from gram-positive bacteria, particularly Bacillus subtilis and Geobacillus stearothermophilus, that challenges the universality of Pol I's functions and reveals lineage-specific adaptations in replication and repair mechanisms. By synthesizing historical perspectives with recent discoveries, this review underscores both the importance of Pol I and the evolutionary diversification of Pol I in bacterial DNA metabolism.

Bacterial DNA replication↗
PubMed1979

Identification of the C. coli dnaK (groPC756) gene product.

The E. coli dnaK (groPC756) gene product is essential for bacteriophage lambda DNA replication. Bacterial DNA segments carrying this gene have been cloned onto a bacteriophage lambda vector. The product of the dnaK gene has been identified on SDS polyacrylamide gels after infection of UV-irradiated E. coli cells. The dnaK gene codes for a polypeptide with an apparent molecular weight of 93,000-Mr. Transducing phages carrying amber mutations in the dnaK gene fail to induce the synthesis of the 93,000-Mr polypeptide chain upon infection of sup+ bacteria, but do so upon infection of supF bacteria. E coli carrying the dnaK756 mutation are, in addition, temperature sensitive for growth at 43 degrees C. It is shown that the dnaK756 mutation results in an overproduction of the dnaK gene product at that temperature.

Bacterial Proteins↗
PubMed1977

Ficellomycin and feldamycin; inhibitors of bacterial semiconservative DNA replication.

The two peptide-like antibiotics ficellomycin and feldamycin impair semiconservative DNA replication but not DNA repair synthesis in bacteria. Specifically both antibiotics cause the accumulation of a 34S DNA species in toluenized Escherichia coli cells which lacks the capability of being integrated into larger DNA pieces and eventually the complete bacterial chromosome. Novobiocin, a known inhibitor of replicative DNA synthesis, was investigated for comparative purposes. The action of this latter antibiotic differs from the ones exerted by ficellomycin and feldamycin in the novobiocin appears to block an event associated with the initiation of Okazaki fragments. The fact that novobiocin impairs DNA gyrase suggests that this enzyme plays an essential role during the initiation of Okazaki pieces.

Anti-Bacterial Agents↗
PubMed1979

Bacterial DNA synthesized under phage control in a DNA-defective Salmonella-mutant and packaged into a special fraction of transducing particles of phage P22.

Lysates of P22 contain a small fraction of transducing particles with bacterial DNA replicated semiconservatively after the time of infection. It was demonstrated that the presence and relative amount of this class of transducing particles was unchanged, if infection of Salmonella occured under a condition nonpermissive for bacterial DNA replication. Analysis of particles with DNA fragments derived from different regions of the Salmonella chromosome indicated that the replication of the bacterial DNA carried by these transducing particles was not initiated specifically at the normal origin for bacterial chromosome replication.

DNA Replication↗
PubMed1977

A new bacterial gene (groPC) which affects lambda DNA replication.

A bacterial mutation affecting lambda DNA replication, called groPC756, has been mapped between the thr and leu bacterial loci. Most of the parental lambda DNA does not undergo even one round of replication in this host. Lambda mutants, call pi, which map in the lambda P gene are able to overcome the inhibitory effect of the groPC756 mutation. It is shown that the mutation at the groPC locus also interferes with bacterial growth at 42 degree C. A lambda-transducing phage,carrying the groPC+ allele, was isolated as a plaque-former on groPC756 bacteria. Upon lysogenization, it restores both the gro+ and temperature resistant phenotypes.

Chromosome Mapping↗
PubMed2026

Origin flexibility governs robust ssDNA engagement by the DnaA initiator.

In model bacteria, initiation of chromosome replication requires engagement of single-stranded DNA by oligomers of the DnaA-family initiator assembled within the origin DNA. Although arrays of double-strand motifs recognized by DnaA are a general feature of the origins, the DnaA-binding single-strand elements are elucidated in only a limited number of species, and the mechanical principles governing their recognition remain elusive. Using the Alphaproteobacterium Caulobacter crescentus, we identify a previously uncharacterized GA-rich single-stranded element in the origin that directly engages DnaA oligomers and is essential for robust initiation. This element is positioned at a subkilobase distance from the DnaA oligomerization region and is brought into proximity through dynamic structural rearrangements. Moreover, DnaA oligomers exhibit an unexpectedly broad yet constrained capacity to accommodate single-stranded sequence variation. These findings provide the molecular basis for origin plasticity, highlighting how origins can diverge while preserving initiation logic.

DNA, Single-Stranded↗
PubMed1978

Identification of a biochemically unique DNA-membrane interaction involving the Escherichia coli origin of replication.

DNA-membrane complexes have been obtained from Escherichia coli by using a freeze-thaw lysis procedure that avoids lysozyme and detergents. Complexes made in this manner and containing DNA near the origin of replication are uniquely sensitive to ionic strength, Pronase, and trypsin. There is approximately one such complex per chromosomal origin. The sensitivities suggest that origin-specific binding is mediated by a protein. By using these unique characteristics to distinguish origin-specific complexes from the majority of DNA-membrane binding sites, it was found that the origin-specific binding persists after termination of chromosomal replication.

Cell Membrane↗
PubMed1978

Organization and expression of the dnaJ and dnaK genes of Escherichia coli K12.

A temperature-sensitive mutation in the dnaJ gene of Escherichia coli K12 is described which affects replication of the bacterial DNA. The gene is located adjacent to the dnaK gene described previously (Saito and Uchida, 1977). The physical and functional organization of the dnaJ-dnaK region was studied in detail by analyzing the heteroduplexes and functions of various deletion mutants of lambdadnaJdnaK, a transducing phage carrying both of the dna genes. The sizes of dnaJ and dnaK cistrons were estimated to be at most 1.2 +/- 0.5 and 2.1 +/- 0.4 kilobases, respectively. In vivo expression of the dnaJ function by various deletion phages indicated that the dnaK and dnaJ cistrons were transcribed from a promoter located at the head of the dnaK cistron, dnaJ being downstream to dnaK. Presence of a weak promoter which reads only the dnaJ cistron was also suggested. A simple method for isolating independent deletion mutants of phage lambda was described.

Chromosome Mapping↗
PubMed1978

Size variations and correlation of different cell cycle events in slow-growing Escherichia coli.

Cell lengths have been determined at which cycle events occur in the slow-growing Escherichia coli B/r substrains A, K, and F26. The radioautographic and electron microscope analyses allowed determination of the variations in length at birth, initiation and termination of DNA replication, and initiation of the constriction process and of cell separation. In all three substrains the standard deviation increased between cell birth and initiation of DNA replication. From there on, the standard deviation remained relatively constant until cell separation. These observations are consistent with the presence of a deterministic phase during the cell cycle in which the cell sizes at initation of DNA replication and at cell division are correlated.

Cell Cycle↗
PubMed1979

Phospholipid synthesis during the cell division cycle of Escherichia coli.

Stepwise changes in the rate of phosphatidylethanolamine and phospholipid synthesis during the cell division cycle of Escherichia coli B/r were observed. The cell ages at the increases were found to be a function of the growth rate. At each growth rate, the increase occurred around the time new rounds of chromosome replication were inaugurated in the cycle.

Cell Cycle↗