Figure 2.

Maintenance of microinjected plasmid DNA. Total DNA was extracted from control uninjected nd7 cells (lane a), cells of a vegetative clone derived from a cell microinjected with pICL1b (lanes b and d), and cells of a postautogamous line derived from the pICL1b transformed clone (lane c). Undigested DNA was fractionated (4–8 μg/lane) on a 1% agarose gel by contour-clamped homogeneous electric field (CHEF) electrophoresis (9 V/cm; switch time, 0.1 s; angle, 120°; run time, 3 h), using a CHEF-DR III apparatus (Bio-Rad, Richmond, CA), and transferred to nitrocellulose. The same filter was sequentially hybridized with the ICL1 ( lanes a–c) and the pUC18 (lane d) specific probes. The 50- to 800-kb Paramecium macronuclear chromosomes are not resolved in these experimental conditions: the weak signals detected in control and postautogamous cells most likely arise from hybridization with the endogenous ICL1 genes.