Enhanced Expression ofS-Adenosylmethionine Synthetase Causes Overproduction of Actinorhodin inStreptomyces coelicolorA3(2)

Abstract

We found that a 46-kDa protein is highly expressed in an actinorhodin-overproducing Streptomyces coelicolor A3(2) mutant (KO-179), which exhibited a low-level resistance to streptomycin. The protein was identified as S-adenosylmethionine (SAM) synthetase, which is a product of the metK gene. Enzyme assay revealed that SAM synthetase activity in strain KO-179 was 5-to 10-fold higher than in wild-type cells. The elevation of SAM synthetase activity was found to be associated with an increase in the level of intracellular SAM. RNase protection assay revealed that the metK gene was transcribed from two distinct promoters (p1 and p2) and that enhanced expression of the MetK protein in the mutant strain KO-179 was attributed to elevated transcription from metKp2. Strikingly, the introduction of a high-copy-number plasmid containing the metK gene into wild-type cells resulted in a precocious hyperproduction of actinorhodin. Furthermore, the addition of SAM to the culture medium induced Act biosynthesis in wild-type cells. Overexpression of metK stimulated the expression of the pathway-specific regulatory gene actII-ORF4, as demonstrated by the RNase protection assay. The addition of SAM also caused hyperproduction of streptomycin in Streptomyces griseus. These findings implicate the significant involvement of intracellular SAM in initiating the onset of secondary metabolism in Streptomyces.

Carbon source regulation of antibiotic production

“…caesius. [199][200][201][202] Although the overall mechanism underlying this activity is not completely understood, the obvious methylation of intermediates leading to the biosynthesis of antibiotics involving SAM provides a strong explanation for the high yield of these compounds. 203 There have been notorious advances in the elucidation of the regulatory mechanisms of antibiotic formation at the biochemical and molecular levels.…”

The aptamer core of SAM-IV riboswitches mimics the ligand-binding site of SAM-I riboswitches

“…riboswitches might be misannotated. Gene regulation of sulfur metabolism is of particular interest in Streptomyces, as SAM levels affect antibiotic production and sporulation in these species (Kim et al 2003;Okamoto et al 2003).…”

Activation of secondary metabolite–biosynthetic gene clusters by generating rsmG mutations in Streptomyces griseus

“…In S. coelicolor, enhanced expression of the metK gene encoding S-adenosylmethionine synthetase corresponds to the enhanced production of streptomycin and actinorhodin caused by rsmG mutations. 5,12 Moreover, addition of S-adenosylmethionine causes overproduction of streptomycin in S. griseus, accompanied by enhanced transcription of adpA and strR. 13,14 We analyzed transcription of metK, adpA and strR, together with several genes involved in biosynthesis of streptomycin (strB1, strF and strD) ( Table 3).…”