Research interests

Chromosome replication is initiated by initiator proteins which bind to origins, form oligomeric complexes, separate the two strands of the double helix, and recruit the helicases and the rest of the replication machinery. Initiation must be regulated in such a way that each segment of DNA is duplicated once, and only once, per generation.

A main actor in proper timing of replication in Escherichia coli is the initiator protein, DnaA. DnaA is a AAA⁺-type protein with structural similarity to archaeal and eukaryotic Orc1/Cdc6 proteins. DnaA is also a transcription factor which interacts with RNA polymerase. The activity of DnaA is regulated by Hda and DnaN (β) (structurally similar to PCNA) and occurs by gradual hydrolysis of active ATP-DnaA to inactive ADP-DnaA as the replisome replicates DNA.

Extra rounds of replication are in E. coli prevented by specific inactivation of new origins by the SeqA protein. SeqA specifically binds new DNA via an epigenetic tag which consists of methylated adenines of GATC sequences. Dam methylase methylates GATC sites throughout the chromosome, except immediately following the replication fork where hemimethylated DNA is protected by the SeqA protein. This epigenetic lable also provides the basis for directing mismatch repair enzymes to the correct DNA strand.

Excess replication causes frequent replication fork collapse which in turn may cause mutations and genomic instability. Several different enzymes and pathways are important in replication fork reactivation and repair, among these the DnaN sliding clamp. A coupling between the number of forks underway and the integrity of the forks seems to exist, possibly affected by enzymes with main roles whithin glycolysis.

Chromosome replication must be coordinated with cell growth. Signals that change initiation frequency in response to changes in growth conditions are so far largely unknown, but are likely to involve quorum sensing factors and small molecules such as the starvation signal ppGpp.

Although most bacterial genomes are composed of a single chromosome, many unicellular organisms also harbour several chromosomes, giving the possibility to study coordinated replication of several chromosomes in simple systems. Vibrio cholerae, the causative agent of cholera has a large and a small chromosome. Apparently the large chromosome governs the replication of the small chromosome.

Company affiliation

Based on knowledge aquired through basic science, an applied science project was developed though funding under the EU 5^th framework. The effort, which is aimed at development of new types of drugs targeting replication proteins, has resulted in the establishment of a small, early stage biotech company DnaAcos A/S situated at BMI in Forskningsparken.