Diversity of the structures and functions of Streptomyces linear genomes

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(1) We revealed that the chromosomal inversion found in Streptomycesgriseus 402-2 occurred by transposition of a transposonfollowedbyhomologousrecombinationbetweenthe old and new transposons.Consequently, we identified chimeric direct repeat sequences at both ends of the two transposons in strain 402-2.(2) We revealed that a series of linear plasmids in S. violaceoruber JCM4979 were formed by amplification of a 36-kb DNA unit comprising of SCP1 and SCP2 fragments in SCP1. It is quite interesting that these linear plasmids are compatible in spite of their identical oriC sequence.(3) The structure of LC-KA05 produced by an amine oxidasemutantof S. rochefindicated that oxidation of an amide intermediate to an imide followed by nucleophilic attack by C2 formed the unique 17-membered ring of lankacidin. Heterologous expression of the Ikc cluster in S. lividans and the lkcFG gene fusion experiment supported our modular-iterative polyketide biosynthesis hypothesis for lankacidin.(4) Feeding and gene targeting experiments revealed that isoleucine was oxidized to 2-methylbutyrate and incorporated into the 8,15-didexylankanolide skeleton, and then hydroxylated at the 15 and 8 positions by LkmK and LkmF, respectively.(5) We revealed that srrX-srrA make a y-butyrolactone-receptor system in S. rochei. The srrX gene showed a positive effect on antibiotic production and a negative effect on spore formation, while, srrA reversed both effects of srrX. Extensive transcriptional analysis confirmed the signaling pathway from srrX through srrA to srrY. We also identified two SrrA binding sites upstream of the srrY gene, which contained a palindromic sequence for GB-receptors and repeat sequences for SARP proteins, respectively.