Concept

Crosslinking of DNA

Résumé
In genetics, crosslinking of DNA occurs when various exogenous or endogenous agents react with two nucleotides of DNA, forming a covalent linkage between them. This crosslink can occur within the same strand (intrastrand) or between opposite strands of double-stranded DNA (interstrand). These adducts interfere with cellular metabolism, such as DNA replication and transcription, triggering cell death. These crosslinks can, however, be repaired through excision or recombination pathways. DNA crosslinking also has useful merit in chemotherapy and targeting cancerous cells for apoptosis, as well as in understanding how proteins interact with DNA. Many characterized crosslinking agents have two independently reactive groups within the same molecule, each of which is able to bind with a nucleotide residue of DNA. These agents are separated based upon their source of origin and labeled either as exogenous or endogenous. Exogenous crosslinking agents are chemicals and compounds, both natural and synthetic, that stem from environmental exposures such as pharmaceuticals and cigarette smoke or automotive exhaust. Endogenous crosslinking agents are compounds and metabolites that are introduced from cellular or biochemical pathways within a cell or organism. Nitrogen mustards are exogenous alkylating agents which react with the N7 position of guanine. These compounds have a bis-(2-ethylchloro)amine core structure, with a variable R-group, with the two reactive functional groups serving to alkylate nucleobases and form a crosslink lesion. These agents most preferentially form a 1,3 5'-d(GNC) interstrand crosslink. The introduction of this agent slightly bends the DNA duplex to accommodate for the agent's presence within the helix. These agents are often introduced as a pharmaceutical and are used in cytotoxic chemotherapy. Cisplatin (cis-diamminedichloroplatinum(II)) and its derivatives mostly act on adjacent guanines at their N7 positions.
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