Transcriptional regulation of photosynthesis operons in Rhodobacter sphaeroides 2.4.1

Our studies, using the methods described, have led to the identification of a number of genes and their products that regulate PS gene expression in R. sphaeroides 2.4.1. Some of these factors are clearly DNA-binding proteins, such as IHF, HvrA (SPB), PpsR, and FnrL; some comprise a two-component regulatory system; and some are sensors, as well as signal generators. The identification of these factors has permitted an understanding of some of the individual regulatory pathways in which they are involved. Table II lists factors so far identified and their salient features. The search continues for additional transcriptional factors that are predicted to exist but have not been discovered to date. Additionally, we have studied and continue to study regulation of the regulators, and we have also begun to purify some of the protein components involved in the regulation of gene expression. This and the use of an R. sphaeroides-specific in vitro transcription-translation system will greatly complement our in vivo studies and allow for the more rapid identification and isolation of other components of this system, strengthening the scope of our biochemical approach, through the manipulation of wild-type as well as mutant proteins. We have also begun to study cross- pathway interactions, to define interrelationships and hierarchies among the so far identified regulators.