title: Identification of genes involved in the butyrolactone autoregulator cascade that modulates secondary metabolism in Streptomyces lavendulae FRI-5.
abstract: The gamma-butyrolactone-autoregulator signalling system is widely distributed across many Streptomyces species and it controls secondary metabolism and/or morphological differentiation. IM-2 [(2R,3R,1'R)-2-1'-hydroxybutyl-3-hydroxymethyl-gamma-butanolide] is a gamma-butyrolactone autoregulator which, in Streptomyces lavendulae FRI-5, switches off the production of D-cycloserine, but switches on the production of several nucleoside antibiotics and blue pigment. In the IM-2 system, an IM-2 specific receptor (FarA) plays a critical role in the biosynthetic regulation of these metabolites, including IM-2 itself. Here, we identified five additional regulatory genes in the farA-flanking region and demonstrated that, in addition to farA, at least two more genes (farR1 and farR2) are involved in the IM-2/FarA system as the direct transcriptional target of FarA. The gel-shift assay revealed that FarA was bound to the upstream region of the four genes (including farR1 and farR2) in an IM-2-dependent manner. The FarA-binding sites were localized by DNase I footprinting to 27- to 33-bp palindromic structures, suggesting that FarA-binding sequences consist of two conserved hexamers separated by six nucleotides. Both farR1 and farR2 were transcribed in a growth-dependent manner, and marked expression was induced in the presence of IM-2, whereas transcripts of other two genes were not detected under the cultivation conditions used. The FarA-binding sites of farR1 and far2 overlap the promoter regions, suggesting that FarA represses the transcription of these two genes in the absence of IM-2 by inhibiting RNA polymerase access.
authors.affiliation: International Center for Biotechnology, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kitani
authors.forename: Aya
authors.initials: A
authors.lastname: Iida
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Izumi
authors.forename: Asa
authors.initials: A
authors.lastname: Maeda
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Yamada
authors.forename: Takuya
authors.initials: T
authors.lastname: Nihira