. Author manuscript; available in PMC: 2010 Jan 12.

Published in final edited form as: Toxicol Appl Pharmacol. 2009 Jan 23;236(2):154–165. doi: 10.1016/j.taap.2008.12.028

Table 3.

The effect of Cr(III) and Cr(VI) ion on the generation of mutations by the DNA synthesome during SV40 origin dependent in vitro DNA replication

Chromium Concentration (μM)		Colonies scored		Mutation frequency (× 10⁻⁴)	Error rate^a (× 10⁻⁵)	Mutation^b fold increase
Chromium Concentration (μM)		Total	Mutant	Mutation frequency (× 10⁻⁴)	Error rate^a (× 10⁻⁵)	Mutation^b fold increase
CrCl₃	0	53,058	58	10.9	0.44	1
	1	50,208	84	16.7	0.68	1.53
	5	48,308	122	25.3	1.02	2.30
	10	47,126	138	29.3	1.19	2.68
	50	42,105	229	54.4	2.20	4.97
	100	12,458	185	148.5	6.01	13.57
Na₂Cr₂O₇	0	43,240	64	14.8	0.60	1
	1	42,840	58	13.5	0.55	0.92
	5	45,728	72	15.7	0.63	1.31
	10	43,289	84	19.4	0.79	1.28
	50	39,456	79	20.0	0.81	1.35
	100	38,870	82	21.1	0.85	1.42

SV40 origin dependent DNA replication assays, mediated by the DNA synthesome, were performed in the absence or presence of a range of concentrations of chromium chloride or sodium dichromate as described in the Methods. Newly replicated pBK-CMV plasmid DNA, containing the LacZα and lac promoter elements was transformed into E. coli cells, and the frequency of mutation was scored by counting the number of white colonies growing on the agar plates and expressing this number relative to the total number of colonies bacterial colonies growing on the plate, (Sekowski et al., 1997, 1998.). The target sequence leading to the creation of white colonies in the pBK-CMV plasmid includes the lac Zα and lac promoter elements (494 bp). The error rate,

represents the relative number of errors created in the target sequence of the nascent DNA during the in vitro DNA replication reaction. The values were calculated by subtracting the background mutant frequency (5×10⁻⁸) from the average mutation frequency, dividing this number by 0.5, and the number of nucleotides (494) within the DNA being sequenced.

Fold increase in mutation frequency was determined by comparing the mutation frequency observed for reactions performed in the absence of chromium ion with those performed in the presence of a range of chromium ion concentrations. The values reported represent the mean of 3 independent experiments.