Table 3. Identification of the platinum chelates formed by reaction of trans-[Pt(NH₃)₂(H₂O)₂]²⁺ 2 with (T₂AG₃)₄ II^a.

Analysis of the platinated fragments from gel bands 2.1, 2.2, 2.3 and 2.4 (Fig. 3)		Platinated sitesb
		A1	A7	G10	A13	A19	G20	G22
% Platinated G	2.1 and 2.3			60			<15	50
(DMS)	2.2			30			<15	30
	2.4			<15			30	30
% Platinated	2.1 and 2.3	45	<15		35	<15
A–N7	2.2	55	85		60	80
(DEPC)c	2.4	<15	<15		<15	<15
3′-Exonuclease	2.1 and 2.3	A1		G10	A13 and G14d			G22
stopd	2.2	A1	A7	G10	A13	A19		G22
	2.4	A1	A7		A13	A19	G20	G22
Platinated	2.1 and 2.3	3		12	15			24
fragment size	2.2	3	9	12	15	21		24
(mer)b	2.4	3	9		15	21	22	24
‘n-mer like’ migration of the platinated fragment after digestion	2.1 and 2.3 2.2 2.4	10 10 10	14 13	11–12e 16–17e	14–15e 14–15e 14 and 17i	19 20	21	18 (2.1) 20 (2.3) 20 23
Base position	2.1 and 2.3	5′		3′	5′f			3′
in the chelate	2.2	5′	5′	3′f	5′ or 3′f	3′		3′
	2.4	5′	5′		5′ and 3′i	3′	3′	3′
Conclusion	2.1 and 2.3	One bis-chelate A1–G10/A13–G22g
	2.2	Three bis-chelates A1–G10/A7–A19; A1–A13/A7–A19 and A13–G22/A7–A19
	2.4h	Four chelates A1–A13; A13–G22; A7–A19; A7–G20

^aSee text for step-by-step analysis.

^bII is a 24mer but for the sake of comparison we have adopted the same base numbering as that of the 22mer I. However, the size of the fragments is the actual one.

^cDEPC/piperidine treatment does not detect A–N1 binding. The lower limit of reliable quantification by gel analysis is 15%.

^dFor some adducts, the 3′-exonuclease exhibits a one nucleotide premature arrest. This is easily detected thanks to the assignment of the platination sites by chemical digestion.

^eThe two values result from the non-identity of the migration scales of the free and platinated fragments.

^fBecause of the presence of another platinum chelate at the 5′ side of this base, its position in the chelate cannot be deduced from the migration length of the digested platinated fragment. This was done thanks to the measured distances between the purine nitrogens in structure A indicating the geometrically feasible chelates (Table 4).

^gThe same bis-chelate is present in products from 2.1 and 2.3. The latter carries a supplementary platinum complex whose binding site has not been identified.

^hMass spectrometry data indicate one platinum per oligonucleotide.

ⁱThe two fragments result from the same A13 digestion stop. See text.