Light-responsive psbA Transcription Requires the −35 Hexamer in the Promoter and Its Proximal Upstream Element, UPE, in Cyanobacteria

Abstract

We characterized the function of the −35 hexamer in the promoter and an element just upstream, UPE, in the expression in a unicellular cyanobacterium, Microcystis aeruginosa K-81, of the light-responsive gene psbA2, which encodes a reaction center key protein for photosynthesis. A series of mutants with mutations at the −35 hexamer (−35 to −30) and a novel conserved upstream element (UPE: −45 to −36, +1 referring to the transcription start point) were constructed. Expression of the mutants was examined in vivo and in vitro by analyses using a β-galactosidase assay, primer extension, and a DNA-mobility shift assay with RNA polymerases. Results indicated that the −35 hexamer and its proximal UPE act as effective cis-elements for the light-responsive and/or basal transcription, respectively. A model of the 5′-upstream region with cis- and possible trans-acting factors is presented for the psbA regulatory system.

• transcription
• RNA polymerase
• sigma factor
• curved DNA
• photosynthesis