Mapping psoralen cross-links at the nucleotide level in mammalian cells: Suppression of cross-linking at transcription factor- or nucleosome-binding sites
J. Komura et al., Mapping psoralen cross-links at the nucleotide level in mammalian cells: Suppression of cross-linking at transcription factor- or nucleosome-binding sites, BIOCHEM, 40(13), 2001, pp. 4096-4105
We have developed a new genomic sequencing method for detecting, with resol
ution at the nucleotide level, the interstrand DNA cross-links induced by 4
,5',8-trimethylpsoralen along single-copy genes in mammalian cells. The cro
ss-links (diadducts) initially formed are converted into monoadducts by alk
ali reversal prior to the use of terminal transferase-dependent PCR (TD-PCR
). After alkali reversal but not before, the DNA strands can be separated a
nd used as templates for gene-specific primer extension, which is the first
step in the TD-PCR procedure. The converted psoralen adducts block primer
extension, and the prematurely terminated single-stranded products are then
amplified by TD-PCR and visualized on a sequencing gel. Adducts formed by
angelicin, a psoralen derivative that forms only monoadducts, were also inv
estigated by use of TD-PCR. Comparison of the adduct distribution patterns
of in vivo-treated DNA with those of in vine-treated DNA revealed that the
binding of transcription factors inhibited both psoralen cross-linking and
angelicin monoadduct formation in the c-JUN and c-FOS promoters in living h
uman cells. Adduct formation was also inhibited in the region of a putative
positioned nucleosome in the c-FOS promoter. These methods should be of ge
neral use for study of in vivo protein-DNA interactions and DNA repair.