S-Adenosylmethionine (SAM) is a well-known methyl donor for the methylation of nucleic acids,proteins,and small molecules in both prokaryotes and eukaryotes.Our previous studies have revealed its novel function as a widespread activator for antibiotic biosynthesis in various Streptomyces species although the underlying molecular events remain unclear.In this study,we studied the mechanism by which SAM activated actinorhodin production in S.coelicolor A3(2) using afsK-disruptant and its complemented strains,including complementation by full length afsK gene or its 1-933 bp N-terminal fragment (afsKN),under the control of the native promoter.