Table 1.

Comparison of ATM Protein Binding to Different DNA Molecules by AFM

DNA	Supercoiled plasmid DNA		Linear DNA		Irradiated plasmid DNA
	Observed	Percent	Observed	Percent	Observed	Percent
Free	91	63.2	109	43.4	175	67.0
Internally bound	53	36.8	52	20.7	86	33.0
End bound	—	—	90	35.9	—	—
N	144		251		261

ATM protein was bound in the presence of supercoiled plasmid DNA, a 660-bp linear DNA PCR fragment, or plasmid DNA irradiated with 150 Gy of ionizing radiation. DNA molecules in 2 μM AFM scans were scored as bound or unbound.