AUTOGENOUS TRANSCRIPTIONAL ACTIVATION OF A THIOSTREPTON-INDUCED GENE IN STREPTOMYCES-LIVIDANS

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, TipA(L), whose N-terminus is similar to a family of eubacterial regulatory proteins represented by MerR. TipA(L) was first purified from induced cultures of S.lividans as a factor which bound to and activated transcription from its own promoter. The tipA(L) gene was overexpressed in Escherichia coli and TipA(L) protein purified in a single step using a thiostrepton affinity column. Thiostrepton enhanced binding of TipA(L) to the promoter and catalysed specific transcription in vitro. TipA(S), a second gene product of the same open reading frame consisting of the C-terminal domain of TipA(L), is apparently translated using its own in-frame initiation site. Since it is produced in large molar excess relative to TipA(L) after induction and also binds thiostrepton, it may competitively modulate transcriptional activation.