Cyanobacteria are prolific producers of specialized metabolites, including polyketides and hybrids thereof. Such compounds are assembled by modular enzymes called polyketide synthases (PKSs), which are encoded within large biosynthetic gene clusters. A cryptic type I/III PKS gene cluster (mks) was recently discovered in Microcystis aeruginosa PCC 7806. Interestingly, the mks cluster is inversely regulated by the hybrid polyketide toxin, microcystin. In order to better understand the role of this cryptic gene cluster, we examined the phylogeny of the mks genes and cloned the entire 20 kb gene cluster in E. coli for subsequent heterologous expression and biochemical studies. Our phylogenetic analysis revealed that the mks cluster is highly conserved within Microcystis strains, but is only distantly related to type I/III PKS clusters from other genera. Sequence analysis and homology modelling suggested that the encoded type III PKS likely produces a resorcinol. Preliminary expression studies in E. coli showed that the mks cluster does not transcribe from the native promotor. Hence, a tetracycline-inducible promoter (pTet) was introduced using homologous recombineering. This promotor exchange significantly improved the transcription of mks genes in E. coli. HPLC analysis revealed a number of unique peaks in cell extracts expressing the mks cluster. Purification and structural characterisation of the corresponding metabolites are underway.