Activity of translation system and abundance of tmRNA during development ofStreptomyces aureofaciens producing tetracycline

Abstract

Transition from exponential phase of growth to stationary phase in Streptomyces aureofaciens is characterized by a decrease in the rate of translation and induction of tetracycline (Ttc) biosynthesis. In exponential phase, no significant changes were found in the activity of ribosomes at binding of ternary complex Phe-tRNA.EF-Tu.GTP to the A-site on ribosomes. Overexpression of Ttc in stationary phase is accompanied by a decrease in the binding of the ternary complex Phe-tRNA.EF-Tu.GTP to the A-site of ribosome and a formation of an aggregate with Ttc by part of the ribosomes. Antibiotics that cause ribosome to stall or pause could increase the requirement for tmRNA in the process called trans-translation. We found differences in the level of tmRNA during the development of S. aureofaciens. Subinhibitory concentrations of Ttc, streptomycin and chloramphenicol induced an increase in the tmRNA level in cells from the exponential phase of growth. In vitro trans-translation system of S. aureofaciens was sensitive to Ttc at a concentration of > 15 micromol/L; the trans-translation system can thus be considered to contribute to resistance against Ttc produced only at sublethal concentrations. These experiments suggest that the main role of the rising tmRNA level at the beginning of the Ttc production is connected with ribosome rescue.

Expression of tmRNA in mycobacteria is increased by antimicrobial agents that target the ribosome

“…The change in ssrA promoter activity suggested that the increased synthesis and levels of tmRNA were an adaptive response to ribosome inhibition. Clearly, this expands on previous studies on the effect of ribosome inhibitors on tmRNA levels in other bacteria (Montero et al , 2006; Paleckova et al , 2006). To our knowledge, this is the first direct study of tmRNA in mycobacteria.…”

“…Increased tmRNA levels were described previously for other bacteria exposed to antimicrobial agents. Montero et al (2006) reported that chloramphenicol increased tmRNA levels up to 40‐fold in the extremophile T. maritima , and Paleckova et al (2006) reported that streptomycin increased tmRNA levels by 2.6‐fold in S. aureofaciens . However, it was not clear from these studies whether the increased tmRNA levels were the result of increased tmRNA synthesis or of a reduction in tmRNA degradation, or both.…”

“…This suggested that trans ‐translation is important to bacteria for overcoming the effects of ribosome‐targeting antimicrobial agents, although it was not clear whether ribosome inhibition by antimicrobial agents altered the rate of trans ‐translation. Evidence that such agents may affect trans ‐translation came from previous studies reporting that ribosome inhibitors caused an increase in the levels of tmRNA in Thermotoga maritima (Montero et al , 2006) and Streptomyces aureofaciens (Paleckova et al , 2006). However, these studies did not determine whether the changes in tmRNA levels were the result of decreased tmRNA degradation and/or increased synthesis.…”

Transfer–messenger RNA controls the translation of cell‐cycle and stress proteins in Streptomyces

“…The main chaperone and stress control protein DnaK Hsp70 links to reduced growth rates and heat‐shock sensitivity (Wickner et al , 1991; Bucca et al , 2003; Guisbert et al , 2004), the drug‐resistance regulators, TipA and UspA, to antibiotic sensitivity (Nystrom & Neidhardt, 1992; Kahmann et al , 2003), the cell‐division activator SsgA and its specific transcriptional activator SsgR to developmental defects (van Wezel et al , 2000; Traag et al , 2004; Noens et al , 2007), the alternative translation factor EF‐Tu3 to nutrient stress (van Wezel et al , 1995) and the global transcriptional regulator and nutrient sensory DasR to oxidative stress, programmed cell death and antibiotic production (Rigali et al , 2006, 2008). Transcription of tmRNA is possibly induced by oxidative stress (Paget et al , 2001) in S. coelicolor , as are dnaK, tipA and dasR (Paget et al , 2001; Paleckova et al , 2006; S.B., B.A.T. and G.P.v W., unpublished data).…”

“…Perhaps the ultimate stress response is development; after nutrient depletion, the underlying vegetative mycelium or substrate mycelium is degraded autolytically to yield the necessary building blocks for the aerial mycelium and spores. Several studies have suggested a function of tmRNA in stress control, such as oxidative stress, heat shock and exposure to antibiotics, although the mechanisms and triggers have not been uncovered (Paget et al , 2001; Braud et al , 2006; Paleckova et al , 2006; Yang & Glover, 2009). In this study, we show that in streptomycetes, specific control of gene expression is the main role of tmRNA, with tmRNA‐mediated trans ‐translation tagging almost exclusively the main stress or developmental proteins, which suggests that tmRNA‐mediated protein tagging has evolved into a specialized translational control system in these organisms.…”