Plus ends

The plus ends of interphase microtubules are directed towards the cell cortex where they probe the inner face of the plasmamembrane (PM). Microtubule plus tips frequently pause at the plasmamembrane. This allows proteins that track the plus tips of MTs interact with proteins at the PM - including those that are responsible for nucleating actin filaments. These interactions also determine the length of the pause. In this manner MTs can direct and maintain cell shape or determine where new sites of cell growth will occur. Note that MTs can also grow along existing MTs and that single microtubules grow outwards more slowly than shrinking microtubules contract away from the PM.