Figure 2

Domain organization and posttranslational processing of mammalian MAP1-family proteins. (a) MAP1A, MAP1B and MAP1S contain microtubule- and F-actin-binding sequences in their carboxyl termini, and additional microtubule-binding sites have been mapped to the amino termini of MAP1A and MAP1B. The first microtubule-binding motif of MAP1A and MAP1B include several basic repeats of the amino-acid sequence KKE. In the case of MAP1A, it has been suggested that sequences in the regions flanking these repeats can bind microtubules by themselves [17]. However, the exact location of all sequences involved in this activity has not been mapped to date. All mammalian family members are cleaved near their carboxyl terminus into heavy and light chains. (b) A schematic representation of the posttranslational processing of MAP1A and MAP1B. Black arrows denote preferential interactions; gray arrows denote possible interactions. Once formed, the light chains of MAP1A or MAP1B can interact with the heavy chains of either MAP1A or MAP1B, but a preference for the MAP1A-derived light chain LC2 to bind MAP1A heavy chain has been noted [11]. A separate gene encodes an additional light chain, LC3, which is also found in mature MAP1A or MAP1B complexes.