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A 6625-base pair transposon, Tn4556, was initially isolated from a Streptomyces strain and a sequence analysis was performed; however, its annotation data remain incomplete. At least three positions were identified as frameshift and base-exchange errors by resequencing. The revised sequence revealed that Tn4556 contains four open reading frames that encode transposase, methyltransferase, isoprenyl diphosphate transferase, and resolvase, respectively. Thirty-eight-base pair inverted repeat (IR) sequences at both ends contained a 1-bp mismatch flanked by a target duplication site, and transposition efficiency was improved by the replacement of imperfectly matched IR-L to perfectly matched IR-L. The detection of Tn4556 transposition was markedly facilitated using a delivery vector carrying a strictly counter-selectable marker for Streptomyces strains.

Background: Genetic tools including constitutive and inducible promoters have been developed over the last few decades for strain engineering in Streptomyces. Inducible promoters are useful for controlling gene expression, however only a limited number are applicable to Streptomyces. The aim of this study is to develop a controllable protein expression system based on an inducible promoter using sugar inducer, which has not yet been widely applied in Streptomyces., Results: To determine a candidate promoter, inducible protein expression was first examined in Streptomyces avermitilis MA-4680 using various carbon sources. Xylose isomerase (xylA) promoter derived from xylose (xyl) operon was selected due to strong expression of xylose isomerase (XylA) in the presence of D-xylose. Next, a xylose-inducible protein expression system was constructed by investigating heterologous protein expression (chitobiase as a model protein) driven by the xylA promoter in Streptomyces lividans. Chitobiase activity was detected at high levels in S. lividans strain harboring an expression vector with xylA promoter (pXC), under both xylose-induced and non-induced conditions. Thus, S. avermitilis xylR gene, which encodes a putative repressor of xyl operon, was introduced into constructed vectors in order to control protein expression by D-xylose. Among strains constructed in the study, XCPR strain harboring pXCPR vector exhibited strict regulation of protein expression. Chitobiase activity in the XCPR strain was observed to be 24 times higher under xylose-induced conditions than that under non-induced conditions., Conclusion: In this study, a strictly regulated protein expression system was developed based on a xylose-induced system. As far as we could ascertain, this is the first report of engineered inducible protein expression in Streptomyces by means of a xylose-induced system. This system might be applicable for controllable expression of toxic products or in the field of synthetic biology using Streptomyces strains.

The end products from starch hydrolysis by amylases have important applications in various industries. Here, two amylases derived from two Streptomyces species that hydrolyze soluble starch from potato produced maltotriose as the primary maltooligosaccharide product. The genes, annotated as putative glycoside hydrolases, were cloned and expressed in Streptomyces lividans. These amylases displayed hydrolysis activity from pH 3 to 9.5 and were not affected by Ca(2+.) Optimal production of maltotriose was between 20 and 30 °C at pH 6.5. At the optimal temperature, both amylases produced maltotriose-rich end products rather than either maltose or maltotetraose.