The <i>dasABC</i> Gene Cluster, Adjacent to <i>dasR</i> , Encodes a Novel ABC Transporter for the Uptake of <i>N</i> , <i>N</i> ′-Diacetylchitobiose in <i>Streptomyces coelicolor</i> A3(2)

Abstract

ABSTRACT N , N ′-Diacetylchitobiose [(GlcNAc) 2 ] induces the transcription of chitinase ( chi ) genes in Streptomyces coelicolor A3(2). Physiological studies showed that (GlcNAc) 2 addition triggered chi expression and increased the rate of (GlcNAc) 2 concentration decline in culture supernatants of mycelia already cultivated with (GlcNAc) 2 , suggesting that (GlcNAc) 2 induced the synthesis of its own uptake system. Four open reading frames (SCO0531, SCO0914, SCO2946, and SCO5232) encoding putative sugar-binding proteins of ABC transporters were found in the genome by probing the 12-bp repeat sequence required for regulation of chi transcription. SCO5232, named dasA , showed transcriptional induction by (GlcNAc) 2 and N , N ′, N ‴-triacetylchitotriose [(GlcNAc) 3 ]. Surface plasmon resonance analysis showed that recombinant DasA protein exhibited the highest affinity for (GlcNAc) 2 (equilibrium dissociation constant [ K D ] = 3.22 × 10 −8 ). In the dasA -null mutant, the rate of decline of the (GlcNAc) 2 concentration in the culture supernatant was about 25% of that in strain M145. The in vitro and in vivo data clearly demonstrated that dasA is involved in (GlcNAc) 2 uptake. Upstream and downstream of dasA , the transcriptional regulator gene ( dasR ) and two putative integral membrane protein genes ( dasBC ) are located in the opposite and same orientations, respectively. The expression of dasR and dasB , which seemed independent of dasA transcription, was also induced by (GlcNAc) 2 and (GlcNAc) 3 .