PARENT SESSION
Posters P3A Bacteriochlorophyll based antenna systems. Abstracts (219-238)

Mechanisms of redox and blue light control of photosystem gene expression in R. capsulatus. Carl Bauer^*,1, ¹ Department of Biology, Bloomington, IN, USA

ABSTRACT- Our laboratory has identified several overlapping regulatory circuits that are responsible for controlling synthesis of the Rhodobacter capsulatus photosystem. One regulatory circuit is responsible for controlling light harvesting and reaction center apoprotein biosynthesis in response to alterations of oxygen. This circuit involves a redox sensitive histidine kinase, RegB, that autophosphorylates only under anaerobic conditions. RegB-P then transfers the phosphate to an aspartate on the DNA-binding response regulator, RegA. RegA-P then subsequently activates photosynthesis gene expression. In vitro studies indicates that RegB contains a redox responding disulfide that when reduced, stimulates autophosphorylation. We have also observed that RegB kinase activity is inhibited by the presence of oxidized quinines which could constitute a second redox input signal. A second regulatory circuit involves an aerobic repressor known as CrtJ. This repressor is responsible for aerobic repression of bacteriochlorophyll, carotenoid and light harvesting-II gene expression. We have observed that CrtJ is activated for DNA binding by forming an intramolecular disulfide bond when exposed to oxygen. This modification stimulates DNA-binding activity, and hence repression, under aerobic growth conditions. A third regulatory circuit involves a flavin containing antirepressor known as AppA. Under dark conditions, AppA binds to CrtJ thereby inhibiting the DNA binding activity of CrtJ. However, light excitation of the flavin in AppA results in a conformational change that inhibits the antirepressing activity of AppA. Collectively, these results provide a working understanding of regulatory circuits that control photosystem synthesis in response to changes in light intensity and oxygen tension.

KEY WORDS: Light regulation, Redox regulation, Photosynthesis gene expression