TABLE 2.

Increased resistance of superinfection by Zeocin selection

Daya	No. of G418-resistant colonies on target cells
	NIH 3T3	PA317	AMIZ
			No selection	Selection
15	7 × 105	3.2 × 104	4.3 × 103	2.3 × 101
54	6 × 104	1 × 104	1.2 × 103	0
78	5 × 105	1.9 × 104	5.6 × 103	0

^aNumber of days after AMIZ cells were cultured in parallel either with or without Zeocin.