Small but powerful: What is the function of the most-strongly induced gene when cyanobacteria encounter darkness?

There are hundreds of small genes of unknown function in bacterial genomes. In our recent study in Current Biology 32, 136-148 (Song et al., 2022a) we have characterized the function of one of them, atpT. This gene encodes the only 48 amino acid protein AtpΘ, which we characterized as a small protein inhibitor of the ATP synthase. Under unfavorable conditions, AtpΘ is expressed and inhibits the reverse reaction of ATP synthase, which burns ATP to transport protons across the membrane. AtpΘ is conserved in cyanobacteria and its function is related to the unique fact that the ATP synthase in cyanobacteria is ultimately driven by the photosynthetic and the respiratory electron transport chains, both located within the same thylakoid membrane system. The gene atpT was first identified in Synechocystis sp. PCC 6803 as norf1 (Mitschke 2011) and later recognized as the single most-strongly induced protein-coding gene when cyanobacteria encounter darkness (Kopf et al., 2014; Baumgartner et al., 2016). We further found that this up-regulation is closely linked to the energy and redox status of the cell, which is largely mediated by changing the stability of the atpT mRNA (Song et al., 2022b) and developed a protocol for the preparation of intact and active FoF1 ATP synthase (Song et al., 2022c).  

Congratulation to Kuo to make this story the topic of his successful PhD thesis! Special thanks go to Sandra Maaß and Dörte Becher from the Department of Microbial Proteomics at the University of Greifswald, to Martin Hagemann from the University of Rostock and to Alicia Muro-Pastor from the Instituto de Bioquimica Vegetal y Fotosintesis, CSIC and the Universidad de Sevilla, Spain, for the great collaboration. We thank the China Scholarship Council for funding Kuo Song through a scholarship grant and the Deutsche Forschungsgemeinschaft for support through the priority program SPP 2002 “Small Proteins in Prokaryotes, an Unexplored World” and the RTG MeInBio – 322977937/GRK2344. Thanks also to Robert Burnap for writing this article on “Bioenergetics: To the dark side and back with cyanobacterial ATP synthase” as a comment on our paper.