“…These include carcinogen specificity for certain bases within specific sequences [Hemminki, 1983;Wilkins, 1984Wilkins, , 1985Benasutti et al, 19881, sequence motifs [Kootstra et al, 19891, and preferential attack of linker vs. core DNA in nucleosomes 0 1994 Wiley-Liss, Inc. [Jack and Brookes, 1982;Kurian et al, 1985;Moyer et al, 19891, and unusual DNA structures such as Z-DNA [Marrot et al, 19871, replication forks [Paules et al, 19881, and other non-B-DNA structures [Kohwi-Shigematsu et al, 1988;Kohwi, 19891. Preferential DNA damage has also been demonstrated within "active" relative to "inactive" chromatin (as defined by differential DNase sensitivity) [Arrand and Murray, 1982;Delcuve et a]., 19881 or native RNA polymerase activity [Yu, 1983a,b], in repetitive relative to bulk DNA [Gupta, 19841, in ribosomal relative to total DNA [Irvin and Wogan, 19851, in matrix-associated relative to non-associated DNA [Obi et al, 19861, at chromosomal fragile sites [Yunis et al, 19871, and at specific chromosomal loci as determined by immunological techniques [Kurth and Bustin, 1985;Oliver0 et al, 19901. However, to date there is still little or no information regarding the distribution of chemically-induced DNA damage at the level of individual genes. The major impediment to examining targeting at this level is principally methodological.…”