During In vivo Chem-seq,[1] cultured cells in medium are treated simultaneously with either a biotinylated version of the small molecule under study or DMSO (as a control) and 1% formaldehyde for the crosslinking of DNA, proteins and small molecules. DNA is then extracted from the cells, sonicated and enriched for regions containing the biotinylated molecule of interest by incubation with streptavidin magnetic beads, which have a very high affinity for biotin. The enriched DNA fraction is then purified, eluted from the beads and subjected to next generation sequencing.