Biomedical subjects

Ole Skovgaard

Publications and source records attributed to Ole Skovgaard.

5 recordsLinked to original sources

PubMed2006

Hda-mediated inactivation of the DnaA protein and dnaA gene autoregulation act in concert to ensure homeostatic maintenance of the Escherichia coli chromosome.

Initiation of DNA replication in Eschericia coli requires the ATP-bound form of the DnaA protein. The conversion of DnaA-ATP to DnaA-ADP is facilitated by a complex of DnaA, Hda (homologous to DnaA), and DNA-loaded beta-clamp proteins in a process termed RIDA (regulatory inactivation of DnaA). Hda-deficient cells initiate replication at each origin mainly once per cell cycle, and the rare reinitiation events never coincide with the end of the origin sequestration period. Therefore, RIDA is not the predominant mechanism to prevent immediate reinitiation from oriC. The cellular level of Hda correlated directly with dnaA gene expression such that Hda deficiency led to reduced dnaA gene expression, and overproduction of Hda led to DnaA overproduction. Hda-deficient cells were very sensitive to variations in the cellular level of DnaA, and DnaA overproduction led to uncontrolled initiation of replication from oriC, causing severe growth retardation or cell death. Based on these observations, we propose that both RIDA and dnaA gene autoregulation are required as homeostatic mechanisms to ensure that initiation of replication occurs at the same time relative to cell mass in each cell cycle.

Adenosine Triphosphatases↗

PubMed2006

Independent control of replication initiation of the two Vibrio cholerae chromosomes by DnaA and RctB.

Although the two Vibrio cholerae chromosomes initiate replication in a coordinated fashion, we show here that each chromosome appears to have a specific replication initiator. DnaA overproduction promoted overinitiation of chromosome I and not chromosome II. In contrast, overproduction of RctB, a protein that binds to the origin of replication of chromosome II, promoted overinitiation of chromosome II and not chromosome I.

Bacterial Proteins↗

PubMed2005

Dam methylation: coordinating cellular processes.

GATC sequences in Escherichia coli DNA are methylated at the adenine residue by DNA adenine methyltransferase (DamMT). These methylated residues and/or the level of DamMT can influence cellular functions such as gene transcription, DNA mismatch repair, initiation of chromosome replication and nucleoid structure. In certain bacteria, unlike E. coli, DamMT is essential for viability perhaps owing to its role in chromosome replication. DamMT has also been implicated as a virulence factor in bacterial pathogenesis. The origin and phylogeny of DamMT, based on sequenced genomes, has been deduced.

Bacterial Physiological Phenomena↗

PubMed2005

Reduced initiation frequency from oriC restores viability of a temperature-sensitive Escherichia coli replisome mutant.

The dnaX gene of Escherichia coli encodes tau and gamma clamp loader subunits of the replisome. Cells carrying the temperature-sensitive dnaX2016 mutation were induced for the SOS response at non-permissive temperature. The SOS induction most likely resulted from extensive replication fork collapse that exceeded the cells' capacity for restart. Seven mutations in the dnaA gene that partly suppressed the dnaX2016 temperature sensitivity were isolated and characterized. Each of the mutations caused a single amino acid change in domains III and IV of the DnaA protein, where nucleotide binding and DNA binding, respectively, reside. The diversity of dnaA(Sx) mutants obtained indicated that a direct interaction between the DnaA protein and tau or gamma is unlikely and that the mechanism behind suppression is related to DnaA function. All dnaA(Sx) mutant cells were compromised for initiation of DNA replication, and contained fewer active replication forks than their wild-type counterparts. Conceivably, this led to a reduced number of replication fork collapses within each dnaX2016 dnaA(Sx) cell and prevented the SOS response. Lowered availability of wild-type DnaA protein also led to partial suppression of the dnaX2016 mutation, confirming that the dnaA(Sx) mode of suppression is indirect and results from a reduced initiation frequency at oriC.

Bacterial Proteins↗

PubMed2002

Genetic organization of the Vibrio harveyi DnaA gene region and analysis of the function of the V. harveyi DnaA protein in Escherichia coli.

The Vibrionaceae family is distantly related to Enterobacteriaceae within the group of bacteria possessing the Dam methylase system. We have cloned, sequenced, and analyzed the dnaA gene region of Vibrio harveyi and found that although the organization of the V. harveyi dnaA region differs from that of Escherichia coli, the expression of both genes is autoregulated and ATP-DnaA binds cooperatively to ATP-DnaA boxes in the dnaA promoter region. The DnaA proteins of V. harveyi and E. coli are interchangeable and function nearly identically in controlling dnaA transcription and the initiation of chromosomal DNA replication despite the evolutionary distance between these bacteria.

Adenosine Triphosphate↗