ABSTRACT
The function of 6S RNA, a global regulator of transcription, was studied in the photosynthetic α-proteobacterium Rhodobacter sphaeroides. The cellular levels of R. sphaeroides 6S RNA peak toward the transition to stationary phase and strongly decrease during extended stationary phase. The synthesis of so-called product RNA transcripts (mainly 12-16-mers) on 6S RNA as template by RNA polymerase was found to be highest in late exponential phase. Product RNA ≥ 13-mers are expected to trigger the dissociation of 6S RNA:RNA polymerase complexes. A 6S RNA deletion in R. sphaeroides had no impact on growth under various metabolic and oxidative stress conditions (with the possible exception of tert-butyl hydroperoxide stress). However, the 6S RNA knockout resulted in a robust growth defect under high salt stress (0.25 M NaCl). Remarkably, the sspA gene encoding the putative salt stress-induced membrane protein SspA and located immediately downstream of the 6S RNA (ssrS) gene on the antisense strand was expressed at elevated levels in the ΔssrS strain when grown in the presence of 250 mM NaCl.
Subject(s)
Adhesins, Bacterial/genetics , Gene Expression Regulation, Bacterial , RNA, Bacterial/genetics , RNA, Messenger/genetics , RNA, Untranslated/genetics , Rhodobacter sphaeroides/genetics , Adhesins, Bacterial/metabolism , DNA-Directed RNA Polymerases/genetics , DNA-Directed RNA Polymerases/metabolism , Gene Deletion , Phenotype , RNA, Bacterial/metabolism , RNA, Messenger/metabolism , RNA, Untranslated/metabolism , Rhodobacter sphaeroides/drug effects , Rhodobacter sphaeroides/growth & development , Rhodobacter sphaeroides/metabolism , Sodium Chloride/pharmacology , Stress, Physiological , Transcription, GeneticABSTRACT
Using gene targeting by homologous recombination in Ceratodon purpureus, we were able to knock out four phytochrome photoreceptor genes independently and to analyze their function with respect to red light dependent phototropism, polarotropism, and chlorophyll content. The strongest phenotype was found in knock-out lines of a newly described phytochrome gene termed CpPHY4 lacking photo- and polarotropic responses at moderate fluence rates. Eliminating the atypical phytochrome gene CpPHY1, which is the only known phytochrome-like gene containing a putative C-terminal tyrosine kinase-like domain, affects red light-induced chlorophyll accumulation. This result was surprising, since no light dependent function was ever allocated to this unusual gene.