The dasABC genes encode an ATP-binding cassette (ABC) transporter, which is one of the uptake systems for N,N'-diacetylchitobiose [(GlcNAc)2] in Streptomyces coelicolor A3(2), although the gene encoding the ABC subunit that provides ATP hydrolysis for DasABC has not been identified. In this study, we disrupted the sequence that is highly homologous to the msiK gene, the product of which is an ABC subunit assisting several ABC permeases in other Streptomyces species. Disruption of msiK severely affected the ability of S. coelicolor A3(2) to utilize maltose, cellobiose, starch, cellulose, chitin and chitosan, but not glucose. The msiK null mutant lacked (GlcNAc)2-uptake activity, but GlcNAC transport activity was unaffected. The data indicated that msiK is essential for (GlcNAc)2 uptake, which in S. coelicolor A3(2) is governed by ABC transporters including the DasABC-MsiK system, in contrast to Escherichia coli and Serratia marcescens, in which (GlcNAc)2 uptake is mediated by the phosphotransferase system. Interestingly, the induction of chitinase production by (GlcNAc)2 or chitin was absent in the msiK null mutant, unlike in the parent strain M145. The defect in chitinase gene induction was rescued by expressing the His-tagged MsiK protein under the control of the putative native promoter on a multicopy plasmid. The data suggest that uptake of (GlcNAc)2 is necessary for induction of chitinase production. The msiK gene was constitutively transcribed, whereas the transcription of dasA [(GlcNAc)2-binding protein gene], malE (putative maltose-binding protein gene), cebE1 (putative cellobiose-binding protein gene) and bxlE1 (putative xylobiose-binding protein gene) was induced by their corresponding sugar ligands. This is believed to be the first report to indicate that (GlcNAc)2 uptake mediated by ABC transporters is essential for chitinase production in streptomycetes, which are known to be the main degraders of chitin in soil.
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