Fluorescent nucleotides and labeling methods using the same

Fluorescent nucleotides useful for labeling nucleic acids which are represented by the formula: X-Y-Z wherein X represents a residue of natural or non-natural nucleotide and the like and binds to Y at a basic moiety of the residue; Y represents a divalent bridging group or a single bond; Z represents a monovalent group derived from a compound represented by the formula (I) wherein R 1 to R 4 represent an alkyl group; V 1 to V 6 represent a hydrogen atom or a substituent; L 1 to L 7 represent a methine group; W represents an oxygen atom, a sulfur atom, -C(R 3 )(R 4 )- or -N(R 5 )- wherein R 3 to R 5 represents an alkyl group; Q represents a nitrogen atom or -C(V 7 )- wherein V 7 represents a hydrogen atom or a monovalent substituent; M represents a counter ion; m represents a number required to neutralize the charge of the molecule; s, t and u represent 0 or 1 or the like, and binds to Y at a reactive group existing in R 1 or R 2 . 1