tmRNA of Streptomyces collinus and Streptomyces griseus during the growth and in the presence of antibiotics.

Streptomycetes are soil microorganisms with the potential to produce a broad spectrum of secondary metabolities. The production of antibiotics is accompanied by a decrease in protein synthesis, which raises the question of how these bacteria survived the transition from the primary to the secondary metabolism. Translating ribosomes incapable to properly elongate or terminate polypeptide chain activate bacterial trans-translation system. Abundance and stability of the tmRNA during growth of Streptomyces collinus and Streptomyces griseus producing kirromycin and streptomycin, respectively, was analysed. The level of tmRNA is mostly proportional to the activity of the translational system. We demonstrate that the addition of sub-inhibitory concentrations of produced antibiotics to the cultures from the beginning of the exponential phase of growth leads to an increase in tmRNA levels and to an incorporation of amino acids into the tag-peptides at trans-translation of stalled ribosomes. These findings suggest that produced antibiotics induce tmRNA that facilitate reactivation of stalled complex of ribosomes and maintain viability. The effect of antibiotics that inhibit the cell-wall turnover, DNA, RNA or protein synthesis on the level of tmRNA was examined. Antibiotics interfering with ribosomal target sites are more effective at stimulation of the tmRNA level in streptomycetes examined than those affecting the synthesis of DNA, RNA or the cell wall.

SsrA genes of streptomycetes and association of proteins to the tmRNA during development and cellular differentiation.

Transfer-messenger RNA (tmRNA, 10Sa RNA, ssrA) is bacterial RNA having both tRNA and mRNA properties and playing an essential role in recycling of 70S ribosomes that are stalled on defective mRNA. The trans-translational system is thought to play a crucial role in bacterial survival under adverse conditions. Streptomycetes are Gram-positive soil bacteria exposed to various physical and chemical stresses that activate specialized responses such as synthesis of antibiotics and morphological differentiation. Comparative sequence analysis of ssrA genes of streptomycetes revealed the most significant differences in the central parts of tag-reading frames, in the stop codons and in the 15-34 nucleotide sequences following stop codons. A major challenge in understanding the interactions that control the function of tmRNA is the definition of protein interactions. Proteins from various phases of development of Streptomyces aureofaciens associated with tmRNA were analyzed. Using affinity chromatography on tmRNA-Sepharose and photo cross-linking experiments with [(32)P]labeled tmRNA seven proteins, the beta and beta'-subunits of DNA dependent RNA polymerase, polyribonucleotide nucleotidyltransferase (PNPase), ribosomal protein SS1, ATP-binding cassette transporters, elongation factor Tu, and SmpB were identified among the proteins associated with tmRNA of S. aureofaciens. We examined the functional role of ribosomal protein SS1 in a defined in vitro trans-translation system. Our data show that the protein SS1 that structurally differs from S1 of Escherichia coli is required for translation of the tmRNA tag-reading frame.