A promoter switch that can rescue a plant sigma factor mutant

Chloroplasts sigma factors act in concert with PEP, the bacterial-type plastid RNA polymerase. Using a sigma knockout line from Arabidopsis thaliana, we investigated mutant-specific changes in plastid gene expression at RNA level. One characteristic feature was the appearance of a long transcript that spans the atpB-E operon and extends considerably into the far-upstream region of atpB. This region reveals a cluster of typical promoter elements for NEP, the second (phage-type) plastid RNA polymerase. The NEP promoter cluster can help maintain RNA synthesis in situations where no functional sigma factor is available for PEP. (c) 2006 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.