Some unusual nucleic acid bases are products of hydroxyl radical oxidationof DNA and RNA

There are over 100 modified bases and their derivatives found in RNA and DN A. For some of them, data concerning their properties, synthesis and roles in cellular metabolism are available, but for others the knowledge of their functions and biosynthetic pathways is rather limited. We have analysed th e chemical structure of modified nucleosides of DNA and RNA considering mai nly their putative synthetic routes. On this basis we suggest, that in addi tion to enzymatic biosynthetic pathways well established for some odd bases , many rare nucleosides can be recognised as products of random chemical re actions. We identify them as primary or secondary products of the reaction of nucleic acids with hydroxyl radicals, the most active oxidising agent in the cell.