THE PEPTIDE SYNTHETASE CATALYZING CYCLOSPORINE PRODUCTION IN TOLYPOCLADIUM-NIVEUM IS ENCODED BY A GIANT 45.8-KILOBASE OPEN READING FRAME

Cyclosporin A, a potent and clinically-important immunosuppressive drug (SandimmunR), is synthesized from its precursor amino acids by cyclosporin synthetase, a single multi-functional enzyme. In this study we report the cloning of the corresponding coding region of this synthetase. It contains an open reading frame of 45.8 kb which encodes a peptide with a calculated M(r) of 1 689 243. The predicted gene product contains 11 amino-acid-activating domains that are very similar to one another and to the domains of other peptide synthetases. Seven of these domains harbour N-methyltransferase functions. This is the largest genomic ORF described so far.