ABSTRACT Alkylating agents are ubiquitously present in the environment, and they can alkylate DNA and RNA directly or after metabolic activation. The focus of the present R35 application is placed on the chemistry and biology of DNA and RNA alkylation, with the overarching goal of understanding the molecular mechanisms through which alkylating agents and other environmental chemicals exert their adverse human health effects. In particular, we will examine the roles of translesion synthesis DNA polymerases in the transcriptional bypass of DNA lesions in cultured human cells, identify DNA damage recognition proteins for alkylated DNA lesions, and investigate their roles in DNA damage response signaling and repair. We will also assess the implications of RNA methylation in the molecular pathology of trinucleotide repeat expansion diseases. The proposed research is a culmination of our established expertise in the areas of DNA damage and repair, proteomics and epitranscriptomics. Completion of the proposed research will lead to an unprecedented level of understanding about the human health consequences of exposure to alkylating agents and other environmental toxicants, and will ultimately result in approaches for the prevention and mitigation of adverse human health consequences arising from environmental exposure.