Table 3 Background and MNNG-induced mutation frequencies in the supF sequence of pS189 shuttle vector plasmids.

Table 1. Background and MNNG-induced mutation frequencies in the supF sequence of pS189 shuttle vector plasmids.Mutation Frequency (%)

Host Cells	MNNG	# of mutant colonies/# of total colonies	Mutation Frequency (%)
NHOK	-	13/25,406	0.051
NHOK	+	33/20,290	0.163
HOK/LXSN	-	12/18,878	0.064
HOK/LXSN	+	37/24,177	0.153
HOK/16E6	-	30/17,294	0.173^a
HOK/16F6	+	105/17,764	0.591^b
HOK/16E7	-	22/18,665	0.118^a
HOK/16E7	+	90/21,846	0.412^b
HOK/16E6/E7	-	33/18,660	0.177^a
HOK/16F6/E7	+	123/18,769	0.655^b
HOK/6bE6	-	18/19,504	0.092^c
HOK/6bE6	+	35/15,368	0.228
HOK/6bE7	-	10/18,972	0.053
HOK/6bE7	+	31/18,843	0.165

^a Significantly different from NHOK (-) group (Binomial comparison of two Poisson rates)

^b Significantly different from NHOK (+) group (Binomial comparison).

^c Not significantly different from NHOK(-) group (Binomial comparison).

Cells transfected with pS189 were exposed to MNNG (1.0 m g/ml) for 2 hours and incubated in fresh medium for 24 hours. The pS189 plasmids were recovered and intro