| Summary: | <p>Abstract</p> <p>Background</p> <p>C-1027, produced by <it>Streptomyces globisporus </it>C-1027, is one of the most potent antitumoral agents. The biosynthetic gene cluster of C-1027, previously cloned and sequenced, contains at least three putative regulatory genes, i.e. <it>sgcR1</it>, <it>sgcR2 </it>and <it>sgcR3</it>. The predicted gene products of these genes share sequence similarities to StrR, regulators of AraC/XylS family and TylR. The purpose of this study was to investigate the role of <it>sgcR3 </it>in C-1027 biosynthesis.</p> <p>Results</p> <p>Overexpression of <it>sgcR3 </it>in <it>S. globisporus </it>C-1027 resulted in a 30–40% increase in C-1027 production. Consistent with this, disruption of <it>sgcR3 </it>abolished C-1027 production. Complementation of the <it>sgcR3</it>-disrupted strain R3KO with intact <it>sgcR3 </it>gene could restore C-1027 production. The results from real time RT-PCR analysis in R3KO mutant and wild type strain indicated that not only transcripts of biosynthetic structural genes such as <it>sgcA1 </it>and <it>sgcC4</it>, but also putative regulatory genes, <it>sgcR1 </it>and <it>sgcR2</it>, were significantly decreased in R3KO mutant. The cross-complementation studies showed that <it>sgcR1R2 </it>could functionally complement <it>sgcR3 </it>disruption <it>in trans</it>. Purified N-terminal His<sub>10</sub>-tagged SgcR3 showed specific DNA-binding activity to the promoter region of <it>sgcR1R2</it>.</p> <p>Conclusion</p> <p>The role of SgcR3 has been proved to be a positive regulator of C-1027 biosynthesis in <it>S. globisporus </it>C-1027. SgcR3 occupies a higher level than SgcR1 and SgcR2 in the regulatory hierarchy that controls C-1027 production and activates the transcription of <it>sgcR1 </it>and <it>sgcR2 </it>by binding directly to the promoter region of <it>sgcR1R2</it>.</p>
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