Dr. Hahn is a Research Faculty member in Dr. David Dubnau’s laboratory.

When starved for essential nutrients, the soil organism Bacillus subtilis has the ability to take up DNA from its environment and, provided there is homology, recombine it into its genome. This process is called transformation. In order for B. subtilis to be transformed it must be in the “K-state”, which is expressed in only 10-20% of a clonal population. The K-state is characterized by transformability and arrested growth compared to non-K-state cells. Phenotypes associated with this growth arrest are a failure to assemble replisomes, a decrease in rRNA synthesis and decreased rate of cell growth. The ComGA protein, which is necessary for DNA binding and assembly of the transformation pilus, is also at least partially responsible for the phenotypes observed in the K-state. Recently, it was demonstrated that ComGA interacts with RelA, the major (p)ppGpp synthetase/hydrolase, and it is proposed that this interaction inhibits the hydrolase activity of RelA, causing an increase in the levels of (p)ppGpp. The concentration of (p)ppGpp increases as cells enter stationary phase, and this molecule is known to decrease rRNA synthesis and result in slower growth. This inhibition of RelA hydrolase activity causes an extended arrest of growth in K-state cells until ComGA is degraded. Since this effect only partially reverses the growth arrest, other proteins must also be involved. Jeanette Hahn’s focus is to identify and characterize these other factors to better understand the growth arrest and how cells escape from the K-state.