RUB »Microbial Biology » Research

1. RNA thermometers

(SPP 1258: Sensorische und regulatorische RNAs in Prokaryoten (only available in German))

Temperature is an important parameter that free-living cells monitor constantly. The expression of heat shock, cold shock and some virulence genes is coordinated in response to temperature changes. Apart from protein-mediated transcriptional control mechanisms, translational control by RNA thermometers is a widely used regulatory strategy. RNA thermometers are complex RNA structures that change their conformation in response to temperature. Most, but not all, RNA thermometers are located in the 5’-untranslated region and mask ribosome binding sites by base-pairing at low temperatures. Melting of the structure at increasing temperature permits ribosome access and translation initiation. We study the structure and function of RNA thermometers of diverse bacteria.

 

2. Regulated proteolysis

(SFB642: GTP- and ATP dependent membrane processes)

The FtsH protease of E. coli controls important cellular processes like the heat shock response and lipopolysaccharide (LPS) biosynthesis by controlled proteolysis of the responsible key factors. Induction of the heat shock response requires the alternative sigma factor RpoH (Sigma32). Degradation of RpoH under non-stress conditions requires FtsH and the DnaKJ chaperone system. Little is known about proteolysis of LpxC, the key enzyme in LPS biosynthesis. We study how the FtsH protease recognizes its substrate and attempt to identify the turnover elements in RpoH and LpxC by genetic and biochemical approaches.

 

3. Bacteria-plant interaction

(SFB 480: Molecular Biology of Complex Functions in Botanical Systems)

Phosphatidylcholine (PC, lecithine) is the major membrane lipid of eukaryotic cells. Only recently it was recognized that many bacteria are capable of synthesizing PC. We found that PC in the membrane of the root-nodulating, nitrogen-fixing bacterium Bradyrhizobium japonicum is required for an efficient symbiotic interaction with soybean plants. We are interested in the molecular details of this interaction and analyze the postulated pathways for PC formation in B. japonicum genetically and biochemically. The role of PC in pathogenic plant-microbe interactions is being studied in Agrobacterium tumefaciens. The genome sequence suggests this bacterium produces PC by two different routes. The respective genes have been disrupted and their contribution to PC biosynthesis and interaction with model plants is under investigation.

 

4. Metal-responsive gene regulation in bacteria

Metals are essential for the catalytic activity of very many enzymes, but are toxic in free form. Hence, bacteria tightly control expression of their metalloenzymes and metal-specific uptake systems.
Since long, our group is interested in molybdenum (Mo)-responsive gene regulation in the photosynthetic bacterium Rhodobacter capsulatus, which is capable of synthesizing a Mo-dependent and a Mo-free nitrogenase, which enable this strain to grow on expense of dinitrogen from air as the sole source of nitrogen. In particular, we are interested in the molecular mechanisms controlling these nitrogenases and a high-affinity Mo transporter.