PATHWAYS FOR TRANSCRIPTIONAL ACTIVATION OF A GLUTATHIONE-DEPENDENT FORMALDEHYDE DEHYDROGENASE GENE

The widespread occurrence of glutathione-dependent formaldehyde dehydr ogenases (GSH-FDH) suggests that this enzyme serves a conserved functi on in preventing the cytogenetic and potentially lethal interaction of formaldehyde with nucleic acids, proteins and other cell constituents . Despite this potential role of GSH-FDH, little is known about how it s expression is regulated. Here, we identify metabolic and genetic sig nals that activate transcription hf a GSH-FDH gene (adhI) in the bacte rium Rhodobacter sphaeroides. Activity of the adhI promoter is increas ed by both exogenous formaldehyde and metabolic sources of this toxin. Elevated adhI promoter activity in Delta GSH-FDH mutants implicates f ormaldehyde or the glutathione adduct that serves as a GSH-FDH substra te, S-hydroxymethylglutathione, as a transcriptional effector. From st udying adhI expression in different host mutants, we find that the pho tosynthetic response regulator PrrA and the tuans-acting spd-7 mutatio n increase function of this promoter. The behavior of a nested set of adhI::lacZ fusions indicates that activation by formaldehyde, PrrA and spd-7 requires only sequences 55 bp upstream of the start of transcri ption. A working model is presented to explain how GSH-FDH expression responds to formaldehyde and global signals generated from the reduced pyridine nucleotide produced by the activity of this enzyme. (C) 1998 Academic Press.