In his Part 2, Chang introduces long noncoding RNAs, or lncRNAs. As their name suggests, lncRNAs are not translated into proteins, and initially their functions were poorly understood. Chang’s group has developed technologies to better understand the function of lncRNAs. For example, his lab characterized the protein partners that interact with Xist, a canonical lncRNA that mediates X chromosome inactivation. They found that the protein Spen is necessary for X chromosome silencing. Interestingly, Spen has likely been co-opted by mammalian cells to inactivate the X chromosome via viral mimicry.