Conversations with NADP

Abstract

Catabolite repression is a central multigene regulatory network that enables bacteria to select and utilize the optimal carbon and energy sources available in a given environment. Cyclic AMP and catabolite gene activator protein (CAP) play central roles in mediating catabolite repression in enteric bacteria but are absent from Gram-positive bacteria, such as Bacillus sp. Instead, catabolite repression is mediated by the binding of catabolite control protein A (CcpA) to catabolite response elements at target genes. Recent data from Kim, Voskuil and Chambliss[1xNADP, corepressor for the Bacillus catabolite control protein CcpA. Kim, J-H., Voskuil, M.I., and Chambliss, G.H. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 9590–9595Crossref | PubMed | Scopus (60)See all References][1]indicate that NADP (but not NAD) significantly enhances CcpA-mediated repression of the α-amylase gene (amyE) of Bacillus subtilis. As NADP carries energy-rich electrons from catabolic reactions to anabolic reactions, this would allow bacteria to coordinate their choice of carbon/energy sources with the energy cycle. The mechanism by which NADP acts as a co-repressor is not clear, but might involve a conformational change in CcpA that alters its interaction with the transcriptional apparatus. Precedent for this comes from studies of the gal operon in Escherichia coli by Chatterjee et al.[2xInteraction of Gal repressor with inducer and operator: induction of gal transcription from repressor-bound DNA. Chatterjee, S. et al. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 2957–2962Crossref | PubMed | Scopus (26)See all References][2]These studies indicate that, during induction of gal transcription by d-galactose, the GalR repressor remains bound to DNA. d-Galactose is thought to block the interaction of GalR with RNA polymerase by altering GalR conformation.