Autogenous transcriptional activation of a thiostrepton-induced gene in Streptomyces lividans.

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Abstract
Although the antibiotic thiostrepton is best known as an inhibitor of protein synthesis, it also, at extremely low concentrations (< 10(−9) M), induces the expression of a regulon of unknown function in certain Streptomyces species. Here, we report the purification of a Streptomyces lividans thiostrepton‐induced transcriptional activator protein, TipAL, whose N‐terminus is similar to a family of eubacterial regulatory proteins represented by MerR. TipAL was first purified from induced cultures of S.lividans as a factor which bound to and activated transcription from its own promoter. The tipAL gene was overexpressed in Escherichia coli and TipAL protein purified in a single step using a thiostrepton affinity column. Thiostrepton enhanced binding of TipAL to the promoter and catalysed specific transcription in vitro. TipAS, a second gene product of the same open reading frame consisting of the C‐terminal domain of TipAL, is apparently translated using its own in‐frame initiation site. Since it is produced in large molar excess relative to TipAL after induction and also binds thiostrepton, it may competitively modulate transcriptional activation.