Open AccessNMR Data Show that the Carcinogen N‐2‐Acetylaminofluorene Stabilises an Intermediate of −2 Frameshift Mutagenesis in a Region of High Mutation Frequency
Author(s) -
Milhé Catherine,
Fuchs Robert P. P.,
Lefèvre JeanFrançois
Publication year - 1996
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1996.00120.x
Subject(s) - heteroduplex , chemistry , 2 acetylaminofluorene , cytosine , guanine , base pair , helix (gastropod) , stereochemistry , mutagenesis , moiety , crystallography , dna , mutation , nucleotide , biochemistry , biology , in vitro , ecology , snail , gene , microsome
The heteroduplex, d(ACC GGCGCC ACA) · d(TGTGG–CCGGT), containing two bulged bases, a cytosine and the guanine G7, either unmodified or modified with the carcinogen N ‐2‐acetylaminofluorene, have been studied by NMR as models of slipped‐mutagenic intermediates (SMI). The melting temperature of the modified heteroduplex is strongly increased compared with that of the unmodified heteroduplex. NMR studies have shown that all the bases of the unmodified heteroduplex are stacked within the helix, without any disruption of the sequential connectivities. The two strands are in a B‐like conformation. Nevertheless, exchangeable‐proton studies have revealed that base pairing is very weak, or even lacking, over two base pairs apart from the bulge. Concerning the modified heteroduplex, no B‐like connectivity is observed in the G5–C9 segment. Moreover, the cytosine C8 is rejected outside the helix, whereas the N ‐2‐acetylaminofluorene moiety is inserted within the helix. The G5 · C18, C6 · G17 and C9 · G16 bases are remarkably stable when the temperature is increased, in agreement with the high melting temperature. Some small unassigned peaks reveal the presence of the minor conformation in equilibrium. The strong stabilisation of the N ‐2‐acetylaminofluorene‐modified heteroduplex compared with the unmodified duplex is in agreement with the high N ‐2‐acetylaminofluorene‐induced mutation frequency compared with the spontaneous frequency and with the hypothesis of mutagenesis occurring during replication.