Bacteria are well adapted to respond to changes in their environment by the differential regulation of gene expression. Regulation at the transcriptional level is mediated, most often, by the binding of specific activator or repressor proteins to. The aim of this joint project is to elucidate the molecular mechanism of gene activation in response to environmental stress. We plan to analyze the function and mechanisms by which integration host factor (IHF), a central protein involved in the formation of higher order nucleoprotein complexes, mediates transcriptional regulation in response to environmental stress. We will investigate two systems, the PL promotor of phage lambda, in E coli which responds to low temperature, and the Pu promotor from the P putida TOL plasmid which responds to the presence of aromatic hydrocarbons. In both of these systems IHF participates in the formation of a complex involving RNA polymerase, an activator and upstream bent. IHF may act in these systems as a chaperone and as an activator interacting with RNA polymerase. The objective of this research is to elucidate the nature and role of specific protein-protein and protein-interactions in the formation of active transcription complexes.