GerE-dependent Transcription in B. subtilis

Emory University, Atlanta GA

Investigators

Abstract

As the bacterium Bacillus subtilis differentiates from the vegetative form into a dormant endospore, complex morphological and physiological changes occur that require the sequential expression of many genes. During the process, new RNA polymerase sigma factors appear (sF,sE,sG,sK), displacing one another in a sequential cascade and conferring on the RNA polymerase a changing specificity for the recognition of different classes of promoters. This mechanism of altering transcriptional specificity is a fundamental element in the regulation of sporulation gene expression. However, during sporulation repressors and activators control the use of some promoters by RNA polymerase containing the sporulation-specific sigma factors. GerE is a DNA binding protein that is required for activation or repression of several specific sK-dependent promoters during the final stage of endospore development. GerE is the smallest member of the LuxR-FixJ family, a widespread, large family of transcriptional activators that includes two-component type response regulators (e.g., DegU, ComA, FixJ, and BvgA) and activators regulated by low molecular weight cofactors (e.g., LuxR and MalT). Most members of the LuxR-FixJ family contain an amino terminal receiver domain linked by a small region to a carboxy-terminal domain that contains an amino acid sequence similar to the helix-turn-helix (HTH) motif found in other DNA-binding proteins and RNA polymerase sigma factors. The 74 amino acid sequence of GerE is similar over its entire length to the DNA binding domain of this protein family, including the HTH motif. Moreover, recently the structure of GerE has been solved by X-ray crystallography. Therefore, GerE provides a simple model for studies of transcription activation by this family. It is not known how GerE stimulates promoter activity. However, the small size of GerE makes it somewhat surprising that it stimulates transcription from various positions at different promoters. The mechanism of GerE-dependent promoter activation will be examined in this project by testing a model in which two specific surfaces of GerE interact with RNA polymerase during activation of the cotC and cotX promoters, respectively. Genetic and biochemical approaches also will be used to test the hypothesis that GerE interacts with sK at some promoters, and with other subunits of sK RNA polymerase at other promoters to stimulate transcription. The results of this project are expected to yield insights into the mechanism of promoter activation by this important family of transcription factors found in a wide variety of bacteria. Because transcription factors play a key role in determining which genes are active in which cells and at what time, their importance cannot be overstated. This project will help us understand how they work.