Overview of the different crosslinking agents discussed in this review and their key features.

Crosslinker	Activation mode	Reaction type	Reversible	Target	Target base & position	Biological applications	In vivo/in vitro
Coumarin	UV, 350 nm	[2+2]	Yes, 254 nm	DNA	T	SNP detection	In vitro
					Base should oppose the crosslinker	Detection and quantification of viral DNA
						DNA methylation
Psoralen	UV, 365 nm	[2+2]	Yes, 254 nm	DNA, RNA	C, T, U	SNP detection	In vitro
					Base should oppose the crosslinker	Antisense	In vivo
						Identification of miRNA targets (miR-TRAP, miR-CLIP)
						DNA methylation
Vinylcarbazole:		[2+2]	Yes, 312 nm	DNA, RNA	C, T, U	Antisense	In vitro
CNVK	UV, 365 nm				Base should be located at position −1 in the complementary strand	DNA methylation	In vivo
CNVD	UV, 365 nm					Detection and identification of miRNA targets
PCX	VIS, 400 nm					FISH
						SNP detection
4-Thiouridines	UV, 365 nm	[2+2]	No	DNA, RNA	C	RNA target identification	In vitro
					Base should oppose the crosslinker
Diazirines	UV, 365 nm	Carbene	No	DNA, RNA	A, C, G, T	Identification of miRNA targets	In vitro
					Reaction with nearby nucleophiles, predominantly with base opposing the crosslinker
Phenylselenide	Dual activation mode:		No	DNA	A	SNP detection	In vitro
	– UV, 350 nm	Radical			Base should oppose the crosslinker
	– Chemical (1O2, NaIO4)	Michael type reaction
Furan	Chemical activation:		No	DNA, RNA	A, C	Detection of DNA and RNA targets	In vitro
	– 1O2	[4+2]			Base should oppose the crosslinker
	– NBS	Nucleophilic addition
Abasic site	Inherently reactive	Nucleophilic addition	No	DNA	A: positioned one nucleotide closer to the 3′ site of the complementary strand	SNP detection	In vitro
					G: positioned one nucleotide closer to the 5′ site of the complementary strand