Nucleosides containing reactive groups (triple bonds) allow the attachment of reporter groups such as biotin or fluorescent dyes by means of click chemistry.

As EdU (5-Ethynyl-2'-deoxyuridine), a nucleoside analog of thymidine, is incorporated by proliferating cells, subsequent incubation of the
cells with fluorescent azide facilitates the direct measurement of de novo DNA synthesis
^[1],[2],[3]. It can be used as a replacement for BrdU (5-Bromo-2'-deoxyuridine). Analog 5-Ethynyl-2'-deoxy-cytidine can be used to
detect DNA synthesis with similar sensitivity as EdU ^[5].

Based on the same principle, 5-EU (5-Ethynyl-uridine) can be used for detection of RNA transcription and turnover in vivo. As it is
incorporated into RNA transcripts, 5-EU-labeled cellular RNA can be detected quickly and with high sensitivity with fluorescent azides ^[4].

   Copper(I) Catalyzed Click Reactions - Background Information and Protocols

Selected references:
[1] Salic et al. (2008) A chemical method for fast and sensitive detection of DNA synthesis in vivo. Proc. Natl. Acad. Sci. USA 105 (7):2415.
[2] Doerr (2008) DNA synthesis lights up. Nature Methods 5 (4):286.
[3] Chehrehasa et al. (2009) EdU, a new thymidine analog for labeling proliferating cells in the nervous system. Journal of Neuroscience Methods 177:122.
[4] Jao et al. (2009) Exploring RNA transcription and turnover in vivo by using click chemistry. Proc. Nat. Acad. Sci. USA 105 (41):15779.
[5] Qu et al. (2011) 5-Ethynyl-2'-deoxycytidine as a new agent for DNA labeling: detection of proliferating cells. Anal Biochem 417(1):112.

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