Driving down the highway, you encounter ever-changing signs -- speed limits, exits, food and gas options. Seeing these roadside markers may cause you to slow down, change lanes or start thinking about lunch. In a similar way, cellular structures called microtubules are tagged with a variety of chemical markers that can influence cell functions. The pattern of these markers makes up the 'tubulin code' and scientists have uncovered the mechanism behind one of the main writers of this code.