GSE159215
Role of a cryptic tRNA gene operon in the recovery from translation stress
As compared to Eukaryotes, Bacteria have a reduced tRNA gene set encoding between 30 and 220 tRNAs, which are thought to act in concert for the maintenance of gene translation. Here we show that in some bacteria the tRNA gene set may be partitioned in a housekeeping sub-set that sustains translation, and an inducible one that is generally silent but can be largely induced to provide functionality under particular conditions. In the model cyanobacterium Anabaena sp. PCC 7120, the inducible set forms an operon encoding 23 functional tRNAs. Transcription of these tRNAs is induced by translation stress, i.e. by insults that impair translation, including antibiotics that target the ribosome. The operon is co-regulated with genes encoding proteins like the tRNA ligase RtcB and the stress-specific protein DpsA, probably involved in a response directed to protect the cell and recover translation. Common regulation suggests participation of operonic tRNAs in this response, although mechanistic issues remain to be determined. Similar long tRNA gene operons were found in species across major bacterial phyla and are shown to be distinct in many aspects from other operons that evolved by gene accretion. Overall design: Cultures of Anabaena (Nostoc) sp. PCC 7120 were grown in triplicate in BG11 medium, treated with 40 µg ml-1 chloramphenicol and incubated under culture conditions. Alliquots were taken 0, 3 ,9 and 24 hours after treatment to extract RNA.