SEQUENCE-SPECIFIC MUTATIONS INDUCED BY N-NITROSODIMETHYLAMINE AT 2 MARKER LOCI IN METABOLICALLY COMPETENT HUMAN LYMPHOBLASTOID-CELLS

N-Nitrosodimethylamine (NDMA) is a potent mutagen and animal carcinoge n to which many people are exposed through the consumption of contamin ated food and the use of tobacco products, Although the mutational spe cificity of NDMA has been studied in bacteria, little is known about t he specific types of mutations induced by NDMA in the human genome, Kn owledge of the mutational spectrum of NDMA in human genes may help to substantiate the role of NDMA in the etiology of human cancers. In the current study, the mutational spectrum of NDMA. was characterized at the tk and hprt loci, in human lymphoblastoid cells capable of metabol ically activating NDMA, A number of patterns were observed among NDMA- induced mutations. At both marker loci, G:C-->A:T transitions dominate d the mutational spectrum of NDMA, which were indicative of the mutage nicity of the O(6)meG lesion. In addition, the majority of G:C-->A:T m utations occurred at guanines 3' to another guanine, Almost all of the se mutations originated on the non-transcribed strand, which suggests that transcription-coupled repair influenced the distribution of G:C-- >A:T transitions at the tk and hprt loci. Furthermore, the observation of hotspots for G:C-->A:T mutations, within both loci, suggests that differential repair kinetics may exist, and consequently affect the di stribution of mutations, Finally, a comparison of the site specificity of G:C-->A:T mutations at the tk and hprt loci, indicated that the ge ne used for mutational analysis influenced the site specificity of NDM A-induced mutations, and possibly reflects the number of 5'-GG-3' site s in the tk and hprt loci that when mutated would yield a mutant pheno type.