Last year, Graumann’s team and their French cooperation partners carried out co-localisation experiments in order to clarify this issue. Their research was based on the observation that the initiation of the copying process becomes confused when the protein YabA is missing. The bacteria start to replicate over and over again when YabA is absent. Does the protein affect the binding of DnaA to the origin of replication and hence the start of the copying process? And if so, how? The researchers coupled the genes for YabA, DnaA and another protein of the replication machinery (DnaX) with different genes encoding proteins of the GFP (green fluorescent protein) family. The proteins then fluoresced different colours in the cell. Under the fluorescence microscope, the biologists were then able to discern the location of the molecules during the replication and cell division process.

"YabA works like an adapter," said Graumann. "It couples DnaA to a component of the replication machinery, thereby arresting the protein." It is still unclear how DnaA detaches from the origin, but Graumann and his team are currently working on the clarification of this point. They assume that another protein, Soj, might be involved as it also appears to play a role in the regulation of initiation. If Soj is not present, then the cell does not know how many replication rounds it has gone through. "Its function might be to remove DnaA following the initiation of DNA," speculates Graumann. "But further experiments are needed to clarify this."

Another question is: how does DnaA initiate replication? Although it is known that DnaA does initiate replication, the scientific question as to how it does this remains unanswered. Graumann and his team are keeping their eye on the ball as far as this question is concerned. Their experiments on molecular replication mechanisms and their regulation in bacteria such as Bacillus subtilis are of great general importance for two reasons: “On the one hand, it is a basic biological process,” said Graumann. “And this, in itself, is of major interest.” On the other hand, the structure and function of DnaA resembles that of known eukaryotic initiator proteins. Therefore, a detailed understanding of the processes at the replication fork in Bacillus subtilis might at some point in the future also provide valuable insights into the replication mechanism of higher organisms. And this could prove to be of major importance for cancer research, as some cancer cells are known to be unable to correctly regulate the number of replications per cell division.