What is a reversible terminator used in next-generation sequencing (NGS)?

A reversible terminator is a modified nucleotide analogous that can terminate primer extension reversibly, which is widely used in NGS techniques with a sequencing by synthesis approach. The termination effect is derived from the blocking groups in the molecule, which can be chemically removed, allowing further extension of the DNA molecule, thus “reversible”. The prime difference between the reversible terminator and dideoxynucleotide employed by Sanger sequencing method is that dideoxynucleotide cannot be further modified, which terminates primer extension irreversibly.