deoxyinosine

Deoxyinosine, abbreviated as dI, is a purine nucleoside consisting of hypoxanthine attached to the sugar 2'-deoxyribose via a beta-N9 glycosidic bond. It is the deoxyribonucleoside counterpart of inosine and is not a standard building block of DNA, but can occur as a damaged or modified lesion in DNA.

In cells, deoxyinosine most commonly arises through deamination of adenine to hypoxanthine, a process that can be promoted by nitrosative or oxidative stress and by certain chemical mutagens. As a result, dI can appear in genomic DNA under conditions that promote hydrolytic or chemical modifications of bases. It is therefore considered a miscoding, mutagenic lesion rather than a normal nucleotide.

Deoxyinosine base-pairs with cytosine more readily than with adenine, and can also pair with other bases under certain conditions. This mispairing tendency can introduce mutations during DNA replication, typically resulting in A:T to G:C transitions if the lesion is not repaired prior to replication. The mutagenic potential of dI depends on the cellular repair capacity and the context within the genome.

Repair and removal of deoxyinosine from DNA involve DNA damage response pathways. A primary repair route is initiated by endonuclease V (nfi), which recognizes inosine in DNA and incises the strand to enable subsequent processing. Other base-excision repair enzymes may also participate in recognizing and removing deaminated purine lesions in some organisms.

Related terms include inosine, the ribonucleoside found in RNA formed by deamination of adenosine. Deoxyinosine is discussed mainly in the context of DNA damage and repair rather than as a standard component of genomic DNA.