The slr1192 (adhA) gene from Synechocystis sp. strain PCC 6803 encodes a member of the medium-chain alcohol dehydrogenase/reductase family. The gene product AdhA exhibits NADP-dependent alcohol dehydrogenase activity, acting on a broad variety of aromatic and aliphatic primary alcohols and aldehydes but not on secondary alcohols or ketones. It exhibits superior catalytic efficiency for aldehyde reduction compared to that for alcohol oxidation. The enzyme is a cytosolic protein present in photoautotrophically grown Synechocystis cells. The expression of AdhA is enhanced upon the exposure of cells to different environmental stresses, although it is not essential for survival even under such stress conditions. The induction of the expression of the adhA gene is dependent on the Hik34-Rre1 two-component system, as it is severely impaired in mutant strains lacking either the histidine kinase Hik34 or the response regulator Rre1. In vitro DNA-protein interaction analysis reveals that the response regulator Rre1 binds specifically to the promoter region of the adhA gene.