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Bacterial amidases are essential to split the shared envelope of adjunct daughter cells to allow cell separation. Their activity needs to be precisely controlled to prevent cell lysis. In

E. coli and many other bacterial species can alter their cell cycle according to nutrient availability. Under optimal conditions bacteria grow and divide very fast but they slow down the cell cycle when conditions deteriorate. This adaptability is underlined by mechanisms coordinating cell growth with duplication of genetic material and cell division. Several mechanisms regulating DNA replication process in E. coli have been described with biochemical details so far. Nevertheless we still don’t fully understand the source of remarkable precision that allows bacterial cells to coordinate their growth and chromosome replication. To shed light on regulation of E. coli DNA replication at systemic level, we used affinity purification coupled with mass spectrometry (AP-MS) to characterize protein-protein interactions (PPIs) formed by key E. coli replication proteins, under disparate bacterial growth conditions and phases. We present the resulting dynamic replication protein interaction network (PIN) and highlight links between DNA replication and several cellular processes, like outer membrane synthesis, RNA degradation and modification or starvation response.ImportanceDNA replication is a vital process, ensuring propagation of genetic material to progeny cells. Despite decades of studies we still don’t fully understand how bacteria coordinate chromosomal DNA duplication with cell growth and cell division under optimal and stressful conditions. At molecular level, regulation of processes, including DNA replication, is often executed through direct protein-protein interactions (PPIs). In this work we present PPIs formed by the key E. coli replication proteins under three different bacterial growth conditions. We show novel PPIs with confirmed impact on chromosomal DNA replication. Our results provide also alternative explanations of genetic interactions uncovered before by others for E.coli replication machinery.

Protein lysine acetylation, regulates a wide range of cellular functions and is controlled by protein deacetylases called sirtuins. In eukaryotes, sirtuins activity is coupled to the spatiotemporally-controlled NAD+ level. However, regulation of the bacterial sirtuin CobB and its coupling to the NAD+ metabolism is not well understood. In this work we show that such coordination in Escherichia coli cells is achieved through a CobB interaction with PRPP synthase Prs, an enzyme necessary for NAD+ synthesis. Probing CobB protein-protein interactions, we demonstrate that it forms a stable complex with Prs. This assembly stimulates CobB deacetylase activity and partially protects it from inhibition by nicotinamide. We provide evidence that Prs acetylation is not necessary for CobB binding but affects the global acetylome and CobB activity in vivo. Consequently, we show that Prs acetylation status affects bacterial growth under different metabolic regimes. Therefore, we propose that CobB-Prs crosstalk orchestrates the NAD+ metabolism and protein acetylation in response to environmental cues.

Bacterial cells often inhabit environments where conditions can change rapidly. Therefore, a lot of bacterial species developed control strategies allowing them to grow and divide very fast during feast and slow down both parameters during famine. Under rich nutritional conditions, fast-growing bacteria can divide with time interval equal to half of the period required to synthesize their chromosomes. This is possible due to multifork replication which allows ancestor cells to start copying genetic material for their descendants. This reproduction scheme was most likely selected for, since it enables maximization of growth rate and hence – effective competition for resources, while ensuring that DNA replication will not become limiting for cell division. Even with this complexity of cell cycle, isogenic bacterial cells grown under defined conditions display remarkably narrow distribution of sizes. This may suggest that mechanisms exists to control cell size at division step. Alternative view, with great support in experimental data is that the only step coordinated with cell growth is the initiation of DNA replication. Despite decades of research we are still not sure what the driving forces in bacterial cell cycle are. In this work we review recent advances in understanding coordination of growth with DNA replication coming from single cell studies and systems biology approaches.

SeqA protein, a main negative regulator of the replication initiation of the Escherichia coli chromosome, also has several other functions which are still poorly understood. It was demonstrated previously that in seqA mutants the copy number of another replicon, the lambda plasmid, is decreased, and that the activity of the lambda p(R) promoter (whose function is required for stimulation of ori lambda) is lower than that in the wild-type host. Here, SeqA-mediated regulation of lambda phage and plasmid replicons was investigated in more detail. No significant influence of SeqA on ori lambda-dependent DNA replication in vitro was observed, indicating that a direct regulation of lambda DNA replication by this protein is unlikely. On the other hand, density-shift experiments, in which the fate of labelled lambda DNA was monitored after phage infection of host cells, strongly suggested the early appearance of sigma replication intermediates and preferential rolling-circle replication of phage DNA in seqA mutants. The directionality of lambda plasmid replication in such mutants was, however, only slightly affected. The stability of the heritable lambda replication complex was decreased in the seqA mutant relative to the wild-type host, but a stable fraction of the lambda O protein was easily detectable, indicating that such a heritable complex can function in the mutant. To investigate the influence of seqA gene function on heritable complex- and transcription-dependent lambda DNA replication, the efficiency of lambda plasmid replication in amino acid-starved relA seqA mutants was measured. Under these conditions, seqA dysfunction resulted in impairment of lambda plasmid replication. These results indicate that unlike oriC, SeqA modulates lambda DNA replication indirectly, most probably by influencing the stability of the lambda replication complex and the transcriptional activation of ori lambda.

Apart from its function as an initiator of DNA replication, the Escherichia coli DnaA protein is also a specific transcription factor. It activates and represses a number of promoters. However, mechanisms of transcription stimulation by DnaA remained unknown. Bacteriophage lambda pR promoter is one of the promoters activated by DnaA. It was reported previously that DnaA binds downstream of the pR promoter and perhaps interacts with the RNA polymerase beta subunit. Here we demonstrate that DnaA positively regulates transcription from pR by stimulation of two steps in transcription initiation: RNA polymerase binding to the promoter region and promoter escape. For this transcription activation, two weak DnaA boxes located downstream of pR are necessary and sufficient. Such a mechanism of transcription activation and location of the activator-binding sites relative to the transcription start point are unusual in prokaryotes. Changes in the distance between the transcription start point and the first DnaA box by 5 and 10 bp and alterations in the orientation of these boxes did not abolish the stimulation of transcription by DnaA, but the efficiency of the promoter activation was different for various mutations. It seems plausible that formation of higher order nucleoprotein structures, involving DNA looping, is necessary for effective stimulation of the pR promoter. At high concentrations, DnaA is a repressor of pR rather than an activator. This repression was found to be because of inhibition of RNA polymerase binding to the promoter region.

To ensure faithful transmission of genetic material to progeny cells, DNA replication is tightly regulated, mainly at the initiation step. Escherichia coli cells regulate the frequency of initiation according to growth conditions. Results of the classical, as well as the latest studies, suggest that the DNA replication in E. coli starts at a predefined, constant cell volume per chromosome but the mechanisms coordinating DNA replication with cell growth are still not fully understood. Results of recent investigations have revealed a role of metabolic pathway proteins in the control of cell division and a direct link between metabolism and DNA replication has also been suggested both in Bacillus subtilis and E. coli cells. In this work we show that defects in the acetate overflow pathway suppress the temperature-sensitivity of a defective replication initiator-DnaA under acetogenic growth conditions. Transcriptomic and metabolic analyses imply that this suppression is correlated with pyruvate accumulation, resulting from alterations in the pyruvate dehydrogenase (PDH) activity. Consequently, deletion of genes encoding the pyruvate dehydrogenase subunits likewise resulted in suppression of the thermal-sensitive growth of the dnaA46 strain. We propose that the suppressor effect may be directly related to the PDH complex activity, providing a link between an enzyme of the central carbon metabolism and DNA replication.

Transcription and DNA replication are tightly regulated to ensure coordination of gene expression with growth conditions and faithful transmission of genetic material to progeny. A large body of evidence has accumulated, indicating that encounters between protein machineries carrying out DNA and RNA synthesis occur in vivo and may have important regulatory consequences. This feature may be exacerbated in the case of compact genomes, like the one of bacteriophage λ, used in our study. Transcription that starts at the rightward pR promoter and proceeds through the λ origin of replication and downstream of it was proven to stimulate the initiation of λ DNA replication. Here, we demonstrate that the activity of a convergently oriented pO promoter decreases the efficiency of transcription starting from pR. Our results show, however, that a lack of the functional pO promoter negatively influences λ phage and λ-derived plasmid replication. We present data, suggesting that this effect is evoked by the enhanced level of the pR-driven transcription, occurring in the presence of the defective pO, which may result in the impeded formation of the replication initiation complex. Our data suggest that the cross talk between the two promoters regulates λ DNA replication and coordinates transcription and replication processes.

Precise regulation of DNA replication is necessary to ensure the inheritance of genetic features by daughter cells after each cell division. Therefore, determining how the regulatory processes operate to control DNA replication is crucial to our understanding and application to biotechnological processes. Contrary to early concepts of DNA replication, it appears that this process is operated by large, stationary nucleoprotein complexes, called replication factories, rather than by single enzymes trafficking along template molecules. Recent discoveries indicated that in bacterial cells two processes, central carbon metabolism (CCM) and transcription, significantly and specifically influence the control of DNA replication of various replicons. The impact of these discoveries on our understanding of the regulation of DNA synthesis is discussed in this review. It appears that CCM may influence DNA replication by either action of specific metabolites or moonlighting activities of some enzymes involved in this metabolic pathway. The role of transcription in the control of DNA replication may arise from either topological changes in nucleic acids which accompany RNA synthesis or direct interactions between replication and transcription machineries. Due to intriguing similarities between some prokaryotic and eukaryotic regulatory systems, possible implications of studies on regulation of microbial DNA replication on understanding such a process occurring in human cells are discussed.

In Escherichia coli hosts, hydrogen peroxide is one of the factors that may cause induction of lambda prophage. Here, we demonstrate that H2O2-mediated lambda prophage induction is significantly enhanced in the oxyR mutant host. The mRNA levels for cI gene expression were increased in a lambda lysogen in the presence of H2O2. On the other hand, stimulation of the p(M) promoter by cI857 overproduced from a multicopy plasmid was decreased in the DeltaoxyR mutant in the presence of H2O2 but not under normal growth conditions. The purified OxyR protein did bind specifically to the p(M) promoter region. This binding impaired efficiency of interaction of the cI protein with the OR3 site, while stimulating such a binding to OR2 and OR1 sites, in the regulatory region of the p(M) promoter. We propose that changes in cI gene expression, perhaps in combination with moderately induced SOS response, may be responsible for enhanced lambda prophage induction by hydrogen peroxide in the oxyR mutant. Therefore, OxyR seems to be a factor stimulating lambda prophage maintenance under conditions of oxidative stress. This proposal is discussed in the light of efficiency of induction of lambdoid prophages bearing genes coding for Shiga toxins.

WE have previously reported a role for the Escherichia coli dnaA gene function in the replication of bacteriophage λ ([Wȩgrzyn et al. 1995][1]). Although in a standard genetic background of E. coli K-12, malfunction of the dnaA gene allowed for lytic development of the phage, regulation of λ DNA

For plasmids derived from bacteriophage lambda, the initiation of bidirectional DNA replication from orilambda depends on the stimulation of transcription from the p(R) promoter by the host replication initiator protein DnaA. Certain Escherichia coli dnaA(ts) mutants cannot be transformed by wild-type lambda plasmids even at the temperature permissive to cell growth. This plasmid-host incompatibility appeared to be due to inefficient stimulation of transcription from the p(R) promoter by the mutant DnaA protein. This paper shows that there is a second mechanism for the incompatibility between lambda plasmids and dnaA(ts) hosts, exemplified in this study by the dnaA46 mutant. This is based on the competition between the lambda P protein and the host DnaA and DnaC proteins for DnaB helicase. Both mechanisms must be operative for the incompatibility.

The chromosomal DNA polymer constituting the cellular genetic material is primarily a device for coding information. Whilst the gene sequences comprise the digital (discontinuous) linear code, physiological alterations of the DNA superhelical density generate in addition analog (continuous) three-dimensional information essential for regulation of both chromosome compaction and gene expression. Insight into the relationship between the DNA analog information and the digital linear code is of fundamental importance for understanding genetic regulation. Our previous study in the model organism Escherichia coli suggested that the chromosomal gene order and a spatiotemporal gradient of DNA superhelicity associated with DNA replication determine the growth phase-dependent gene transcription. In this study we reveal a general gradient of DNA thermodynamic stability correlated with the polarity of chromosomal replication and manifest in the spatiotemporal pattern of gene transcription during the bacterial growth cycle. Furthermore, by integrating the physical and dynamic features of the transcribed sequences with their functional content we identify spatiotemporal domains of gene expression encompassing different functions. We thus provide both an insight into the organisational principle of the bacterial growth program and a novel holistic methodology for exploring chromosomal dynamics.