S-adenosylmethionine synthetase genes from eleven marine dinoflagellates

Paralytic shellfish poisoning toxins (PSTs) such as saxitoxin are believed to be synthesised from precursor molecules including arginine, S-adenosylmethionine (SAM) and acetate. The enzyme SAM synthetase is a good candidate as an early acting enzyme in the PST biosynthetic pathway. We have used degenerate PCR to identify the gene encoding SAM synthetase, Sam, in dinoflagellates. Several different PCR products were cloned and sequenced from PST-producing strains of the dinoflagellates Alexandrium minutum, A. catenella and Gymnodinium catenatum and primers specific to dinoflagellate Sam used for further sequence analysis in 11 species of toxic and nontoxic dinoflagellate genera, including: Alexandrium, Gymnodinium, Karenia, Karlodinium, Noctiluca, Prorocentrum and Takayama. At the nucleotide level, Sam clones were unique to dinoflagellates and the most commonly identified Sam was highly conserved between dinoflagellate species. Dinoflagellate Sam G + C content was both typical (60.8%) or lower (40.7%) compared to A. tamarense. The derived protein sequences showed a low and equal level of similarity to Sam from other species representing a range of Kingdoms. DNA sequence information for dinoflagellate Sam provides important insights for dinoflagellate codon usage, which will facilitate primer design to target novel dinoflagellate genes.