ИСТИНА

E. coli 6S RNA was one of the first discovered non­coding RNAs. It forms a complex with the housekeeping RNA polymerase (RNAP) holoenzyme. The important finding was that RNAP utilizes 6S RNA as a template for the transcription of short product RNAs (pRNAs). We analyzed the expression and function of 6S RNA in α- proteobacterium R. sphaeroides that is a common model organism to study regulated formation of photosynthetic complexes and the response to (photo)oxidative stresses. R. sphaeroides 6S RNA was shown to have a unique expression pattern: it peaks at the end of exponential growth and strongly decreases during prolonged stationary phase. According to our Northern blot analyses, the levels of pRNAs are the highest in mid­to­late exponential phase and largely decrease toward prolonged stationary phase. This trend is also seen in the pRNA­Seq data; 12 to 16­ meric pRNA are assumed to be long enough to remain bound to 6S RNA and to rearrange its structure which triggers RNAP release. It is shown that E. coli and B. subtilis cells lacking 6S RNA worse or better survive at some stress conditions. For R. sphaeroides we found the retarded growth phenotype of the 6S RNA deletion strains under high salt conditions, which can be explained by the dysregulated expression of SspA salt stress protein. The spatial vicinity of ssrS and sspA genes may also point to an interesting mechanistic scenario: newly transcribed 6S RNAs may bind to the same RNAP by which they were synthesized to reduce the frequency of incidences where an RNAP (after transcription of 6S RNA)reinitiates transcription at the nearby promoter that drives sspA expression. This work was supported by the Russian Science Foundation (project No. 14­24­00061).