Silent information regulators are NAD(+)-dependent enzymes that display differential specificity toward acetylated substrates. This report provides first evidence for deacetylation activity of CobB1 in Streptomyces coelicolor. The protein is highly conserved in streptomycetes. The CobB1 protein catalytically removes the acetyl group from acetylated bovine serum albumin. In the absence of NAD+ or when NAD+ was substituted with nicotinamide, deacetylation was stopped. We isolated gene encoding AcetylCoA synthetaseA. The recombinant enzyme produces Acetyl-CoA from acetate. The highest acsA-mRNA level was detected in cells from the exponential phase of growth, and then decreased in transition and stationary phases of growth. Acetylated acsA loses the ability to transfer acetate to CoA. Deacetylation of the enzyme required CobB1, ATP-Mg2, and NAD+. Using specific antibodies against acetylated lys, CobB1, and acsA, we found relationship between level of CobB1 and acetylation of acsA, indicating that CobB1 is involved in regulating the acetylation level of acsA and consequently its activity. It was found that 1-acetyl-tetrahydroxy and 1-acetyl pentahydroxy antraquinone inhibit the deacetylation activity of CobB1.
We report the results of cloning genes for two key biosynthetic enzymes of different 5-aminolevulinic acid (ALA) biosynthetic routes from Streptomyces. The genes encode the glutamyl-tRNA Glu reductase (GluTR) of the C 5 pathway and the ALA synthase (ALAS) of the Shemin pathway. While Streptomyces coelicolor A3(2) synthesizes ALA via the C 5 route, both pathways are operational in Streptomyces nodosus subsp. asukaensis, a producer of asukamycin. In this strain, the C 5 route produces ALA for tetrapyrrole biosynthesis; the ALA formed by the Shemin pathway serves as a precursor of the 2-amino-3-hydroxycyclopent-2-enone moiety (C 5 N unit), an antibiotic component. The growth of S. nodosus and S. coelicolor strains deficient in the GluTR genes (gtr) is strictly dependent on ALA or heme supplementation, whereas the defect in the ALAS-encoding gene (hemAasuA) abolishes the asukamycin production in S. nodosus. The recombinant hemA-asuA gene was expressed in Escherichia coli and in Streptomyces, and the encoded enzyme activity was demonstrated both in vivo and in vitro. The hemA-asuA gene is situated within a putative cluster of asukamycin biosynthetic genes. This is the first report about the cloning of genes for two different ALA biosynthetic routes from a single bacterium.
The aim of this study was to contribute to clarifying the role of 6S RNA in the development and control of antibiotic biosynthesis in Streptomyces coelicolor. Due to the low energetic cost of gene silencing via 6S RNA, it is an easy and rapid means of down-regulating the expression of specific genes in response to signals from changes in the environment. The expression of 6S RNA in S. coelicolor is not constitutive, and its accumulation is adapted to changes in nutritional conditions. The 6S RNA of S. coelicolor is capable of interacting with RNA polymerase β β' subunits and is a template for the transcription of short pRNAs. Deletion of the ssrS gene from S. coelicolor affects the growth rate and causes changes in the expression of several pathway-specific genes involved in actinorhodin biosynthesis. The complementation of the ΔssrS strain with ssrS gene restored the wild-type levels of growth and actinorhodin production. We conclude that 6S RNA contributes to the optimization of cellular adaptation and is an important factor involved in the regulation of growth and expression of key genes for the biosynthesis of actinorhodin.
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