Reduced representation bisulfite sequencing (RRBS) is a method of identifying methylation of nucleotides in DNA.
This method is very similar to bisulfite sequencing, converting unmodified cytosines to uracil and then sequencing, however a restriction enzyme is used to cut out only the CpG islands (where the majority of the modifications are found). This vastly reduces the quantity of sequencing required, which was especially beneficial when DNA sequencing was expensive and time consuming. (This is less of an issue today with high-throughput sequencing technology having a considerably lower cost).
Bisulfite sequencing uses bisulfite conversion to convert unmethylated cytosine nucleotides to uracil, by adding sodium bisulfite.
This method is largely redundant now that PacBio and Oxford Nanopore sequencing technologies are highly accurate and becoming more widely available. This is due to these methods enabling the identification of methylation during their normal use, and bisulfite conversion is no longer necessary. With PacBio sequencing, methylated cytosine nucleotides cause a pause in the incorporation of subsequent bases at the DNA polymerase. This is observed by the optical sensor in the zero-mode waveguide. During Nanopore sequencing, methylated cytosines have a different electron signature when passing through the pore protein (CsgG), enabling methylation to be identified during the normal sequencing process with no additional preparation steps.