In order to put readings and their mutations in context we use a reference sequence and feature table. This enables mutations to be reported using positions defined by the reference sequence, and also allows the effect of the mutations to be noted. To facilitate this gap4 is able to store entries from the EMBL sequence library complete with their feature tables. These feature tables are converted to gap4 database annotations (tags), which means that they can be selectively displayed in the template display and editor, and used to translate only the exons (in the correct reading frame). The reference sequence can be designated (or reassigned) by right clicking on its name. Once set it should appear labelled "S" at the left edge of the editor.