In our proposed project, we will study in great detail the regulatory mechanisms involved in a complex process i.e. the iron homeostasis in cyanobacteria. Notably, the accurate reconstruction of regulatory networks is one of the most challenging tasks in current molecular biology.

Since components of the regulatory network of iron homeostasis are likely to be highly interconnected in a complex manner and thus are difficult to study separately, we propose a systems biology approach based on following principles:
• Iterative scheme: We will apply computational and experimental approaches in an iterative and integrated manner. After an initial in silico construction of the regulatory network (TASK 1), the resulting network will be experimentally validated, enlarged by newly identified components and computationally further evaluated (TASK 2 & 3).
• Multiple approaches and scales: The complexity of the regulatory network cannot be captured by a single computational or experimental method. Thus, a large variety of approaches will be applied both to capture the global transcriptional response to changes of external iron concentrations (TASK 2) and to characterize in detail the dynamics of the core regulators (TASK 3 & 4).
• From qualitative to quantitative: Clearly, an ultimate objective of systems biology is the construction of accurate quantitative models. However, this can be only achieved if a reliable qualitative model exists. Thus, in the proposed project aims, we focus first on qualitative characterization (TASK 1 & 2) and only subsequently on quantitative models of the regulatory network for iron homeostasis in cyanobacteria (TASK 3 & 4).