Growth-phase dependent expression of the mevalonate pathway in a terpenoid antibiotic-producing Streptomyces strain.

Streptomyces griseolosporeus MF730-N6, a terpenoid antibiotic-terpentecin (Tp) producer, has both the nonmevalonate and mevalonate pathways for the formation of IPP. The Tp biosynthetic gene (ter) and the mevalonate pathway gene cluster (mev) including an HMG-CoA reductase gene (hmgr) had previously been cloned from strain MF730-N6. In this study, two distinct dxs genes (dxs 1 and dxs 2) and a dxr gene, which encode DXP synthases and DXP reductoisomerase, and participate in the initial and the second step of the nonmevalonate pathway, respectively, were cloned. These gene products were expressed in E. coli and confirmed to have the expected activities. The dxs 1, dxs 2, dxr, mev, and ter genes were used for Northern blot and primer extension analyses to examine temporal expression of these genes together with a gap gene coding for GAP dehydrogenase, which was also cloned in this study and used as an internal control. Transcripts of the dxs 1, dxs 2, dxr, and gap genes were detected throughout the cultivation. On the other hand, messages of the mev and ter genes were not detected at early growth phase but appeared when Tp production started. These results suggested that the nonmevalonate pathway and the mevalonate pathway were mainly used for the primary metabolism and the secondary metabolism, respectively, and that both of the two dxs genes were actually transcribed in this strain.