One of the 4 Constituent Bases of Nucleic Acids

This page is the CodyCross answer for the clue below from London, Group 494, Puzzle 5 (Barbara Windsor).

Question is: One of the 4 Constituent Bases of Nucleic Acids

and the answer is: GUANINE

Word Meaning:

GUANINE — (chemistry) A substance first obtained from guano; it is a nucleic base and pairs with cytosine in DNA and RNA (by means of three hydrogen bonds).

Definitions from Wiktionary.