Schematic outline of different classes of MAPs and TAPs
α- and β-tubulin isotypes are generated as monomers (α-tubulin: red balls, β-tubulin: green balls). These subunits fold and then they interact to form functional, assembly-competent tubulin dimers with the help of various types of chaperones, which are a prime example of a class of TAPs. Other TAPs are also present in the cellular cytoplasm and bind tubulins for various reasons. Tubulins assemble into MTs. One growing MT is schematically indicated, with its plus (+) and minus (-) ends. MAPs regulate MT behaviour and are often categorized by their mode of binding. Indicated are ‘classic’ MAPs that bind along the MT lattice, +TIPs and -TIPs, which accumulate at growing plus and minus ends, respectively, and motor proteins, which transport cargo along MTs.