Research Projects

One of the suspected human carcinogens that come from the diesel exhaust and causes the air pollution is 3-nitrobenzanthrone (3-NBA) (Scheme 1). It has been estimated that the presence of 3-NBA in urban air levels are in the range of 0.6-6.6ppm. 3-aminobenzanthrone (3-ABA) is a metabolite of 3-NBA, was detected in workers who are routinely exposed to diesel emissions. Previous radiolabelling studies have shown that rat liver microsomes (RLM) activate the 3-ABA, attacks the purine bases and forms three major covalent DNA adducts, viz., dG-C8-ABA, dG-N2-ABA and dA-N6-ABA. These covalent ABA-DNA adducts induce different types of mutations in the bacterial as well as mammalian cells. dG-C8-ABAadducts induces G to T and G to A base substitutions, while dG-N2-ABA and dA-N6-NBA adducts induces G to T and A to G transition mutations, respectively. Further, the mutational outcome varies between the human and bacterial cells that are equipped with replicative machinery. Extensive reports on dG-C8-ABAhave shown that it blocks the DNA replication and causes mutations effectively compared to other two ABA adducts. However, TLS activity differs between the human and bacterial cells. The rate of translesion synthesis (TLS) over dG-N2-ABA is reduced drastically in bacterial cells under SOS-induced condition compared to C8 adduct. Here, we propose to look at the thermodynamics and the mutational pattern of dG-N2-ABA and dA-N6-ABA adducts. The modification of oligonucleotides sequences in different sequence context (different flanking bases and NarI, mutational hotspots sequences) will be carried out. The effect of these adducts on thermodynamic parameters of DNA will be ascertained using biophysical assays. Tandem mass spectrometry and primer extension assays will be used to evaluate the effect of adducts on DNA synthesis and compared with dG-C8-ABA adducts. We will also assess the effect of the modified site on natural DNA synthesis by replicative and translesion DNA polymerases using a combination of structural and biochemical tools. The envisaged outcome of this work will provide complete outlook of the three major nitrobenzanthrone adducts (dG-C8-ABA, dG-N2-ABA and dA-N6-ABA).