Figure 1.

Experimental design for the production of extrachromosomal HMR circles. (A) Organization of cassettes for excision of the native HMR locus, consisting of the a1 and a2 genes, as well as the E and I silencers (not drawn to scale). Relevant landmarks are defined graphically at the top of the figure. Endpoints of the silent chromatin domain were drawn arbitrarily. The right-hand RS site in the simple excision cassette disrupts a pair of overlapping Ty1 solo ∂ elements, entirely deleting one (*) that is present in the W303 but not S288C background. (B) Flow charts of the M and G1 excision protocols. Temporary G1 arrest was achieved with α-factor mating pheromone. M-phase arrest was achieved with microtubule destabilizing drugs (see Materials and Methods).