Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for updating a molecular database. In one aspect, a method includes: receiving data representing a sequence of molecular nucleotides, where the data specifies a base of each molecular nucleotide and synthetic modifications to one or more components of one or more molecular nucleotides in the sequence; generating a user interface presentation that presents: i) for each base in the sequence, a base character that represents the base of the molecular nucleotide, and ii) for each of the one or more molecular nucleotides having one or more components that are synthetically modified, a group of symbols adjacent to the base character that represents the base of the molecular nucleotide, where each symbol in the group of symbols represents a respective synthetic modification; and providing the user interface presentation to a user device for display to a user.