Accurate prediction of the Aspergillus nidulans terrequinone gene cluster boundaries using the transcriptional regulator LaeA

LaeA is a regulatory protein of the genus Aspergillus which controls global expression of secondary metabolism gene clusters. During a previous genome-wide transcriptional profiling screen, numerous novel gene clusters were found to be regulated by LaeA including a cluster required for the production of the antitumor agent terrequinone A. Beginnings and ends of secondary metabolite gene clusters are difficult to predict by gene sequence alone, but sharp demarcation of transcriptional control by LaeA suggested this protein might present a tool to identify cluster ends. To address this possibility in a first test case, we created null mutants of three genes, one regulated and two not regulated by LaeA, lying at the first, sixth and seventh position of a contiguous seven gene region where the third gene in this continuum was already shown to be required for terrequinone A production. Only the gene regulated by LaeA, tdiE, sixth in the series, was required for terrequinone A. In this pilot experiment, these findings experimentally validate LaeA-based predictions of the terrequinone biosynthetic locus boundaries. Further, this study identifies TdiE as a protein of unknown yet essential function for terrequinone A biosynthesis.