title: Multiple alternate transcripts direct the biosynthesis of microcystin, a cyanobacterial nonribosomal peptide.
abstract: The mcyABCDEFGHIJ gene cluster of Microcystis aeruginosa encodes the mixed polyketide synthase/nonribosomal peptide synthetase (microcystin synthetase) which is responsible for biosynthesis of the potent liver toxin microcystin. The sequence and orientation of the mcy genes have previously been reported, but no transcriptional analysis had been performed prior to this study. The mcyABCDEFGHIJ genes are transcribed as two polycistronic operons, mcyABC and mcyDEFGHIJ, from a central bidirectional promoter between mcyA and mcyD. Two transcription start sites were detected for both mcyA and mcyD when cells were exposed to light intensities of 68 and 16 micromol of photons m(-2) s(-1). The start sites, located 206 and 254 bp upstream of the translational start for mcyD under high and low light conditions, respectively, indicate long untranslated leader regions. Putative transcription start sites were also identified for mcyE, mcyF, mcyG, mcyH, mcyI, and mcyJ but not for mcyB and mcyC. A combination of reverse transcription-PCR and rapid amplification of cDNA ends was employed throughout this work, which may have been one of the first transcriptional analyses of a large nonribosomal polyketide gene cluster.
authors.affiliation: School of Microbiology and Immunology, University of New South Wales, Sydney 2052, Australia.
authors.forename: Melanie
authors.initials: M
authors.lastname: Kaebernick
authors.forename: Elke
authors.initials: E
authors.lastname: Dittmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Börner
authors.forename: Brett A
authors.initials: BA
authors.lastname: Neilan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D052998:Microcystins; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005810:Multigene Family; D010453:Peptide Synthases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D052998:Microcystins; D009097:Multienzyme Complexes; D010456:Peptides, Cyclic; C078588:microcystin; D010453:Peptide Synthases; C432283:microcystin synthetase A