A cartoon demonstrating how patterns of co-evolution in linear sequence can be used to predict structure. On the left is an alignment of linear sequences from many different organisms of the same protein. Notice whenever there is a red amino acid on the left (grey box) there is always a complementary green amino acid on the right (and vise versa). This would indicate these two positions likely form a physical interaction, allowing us to draw the two structures on the right. (Cartoon by Sergey Ovchinnikov, UW)