Isolation and characterization of a non-reducing polyketide synthase gene from the lichen-forming fungus Usnea longissima |
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Authors: | Yi Wang Jung A Kim Yong Hwa Cheong Young Jin Koh Jae-Seoun Hur |
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Institution: | (1) Korean Lichen Research Institute, Sunchon National University, Sunchon, 540-742, South Korea; |
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Abstract: | Usnea longissima has long been used as a traditional medicine in China, India, Turkey, Canada and Europe. This lichen can produce several
bioactive compounds that primarily belong to the polyketide family. The enzymes responsible for the production of these compounds
are the polyketide synthases, but the biosynthetic processes in lichens are still unclear. In this study, a cultured mycobiont
of Usnea longissima was used to isolate and characterize a polyketide synthase gene (UlPKS1). Complete sequence information regarding UlPKS1 (6,468 bp) was obtained by screening a Fosmid genomic library using a 512-bp fragment corresponding to part of the ketosynthase
(KS) domain. Sequence analysis of UlPKS1 suggested that it contained features of a non-reducing fungal type I PKS with a starter unit of ACP transacylase (SAT), ketosynthase
(KS), product template (PT), acyl carrier protein (ACP) transacylase, acyltransferase (AT) and thioesterase (TE) domain, and
had five intervening introns. The domain organization of UlPKS1 (SAT-KS-AT-PT-ACP-ACP-TE) was quite similar to that of aromatic
PKSs, and phylogenetic analysis showed that UlPKS1 belonged to the clade of lichenized fungal non-reducing PKS. RT-PCR analyses revealed that the expression of UlPKS1 was down-regulated by glycine and high concentrations of sorbitol, inositol and fructose and up-regulated by sucrose and
glucose. Here, we introduce a non-reducing PKS gene in the lichen-forming fungus U. longissima, with a domain structure similar to the structure of orsellinic acid synthase A (OrsA) which is required for orsellinic acid biosynthesis in Aspergillus nidulans. |
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