Figure 1.

Methodology for production of extrachromosomal DNA rings. A fragment of internal coding sequence of the LYS2 gene was flanked by tandemly oriented RS sites (half-filled rectangles) and integrated at HMR or LYS2. Cross-hatches in the figure indicate the potential for Sir-mediated repression. Induction of the R recombinase gene creates a 2,465-bp extrachromosomal ring, rKWD50N.