Figure 5.

Gene activation events occur in the absence of selection. The cultivation and selection process can be divided into three phases: the early stage (lag and log phases of growth in the absence of selection), the late stage (stationary growth phase in the absence of selection) and the selection phase (growth on solid medium in the presence of the antibiotic). Only at the early stage, a single activation event can lead to more than one zeocin-resistant colony. Six and three resistant colonies were obtained from cultures 13 (A5) and 16 (A6), respectively, and all colonies from one culture showed the same molecular rearrangement, strongly suggesting that the colonies go back to one and the same gene activation event (and that this event occurred early in the absence of antibiotic selection).