Figure 4.1 Kinesin complex. Illustration of the conventional kinesin heavy chain dimer showing the proposed domain architecture.In general, the majority of KIFs have a globular motor domain, incorporating an ATPase site and a microtubule binding motif, termed the “head” (Fig. 4.1). The hydrolysis of ATP by the head results in the translocation of the kinesin molecules along the microtubule substrate with directionality (normally towards the plus end of microtubules). The motor domain itself is relatively well conserved amongst the KIFs, but other regions are variable reflecting the varied roles and associated proteins and light chains of the different kinesins. Generally the kinesin heavy chains dimerise via their stalk regions, although there are examples of monomeric and heterodimeric kinesin complexes. Cargoes are found bound through the highly variable tail regions, either directly or indirectly through light chain or associated proteins.207-209 4.1.1 NomenclatureThe original nomenclature for KIFs (pre 2004) was dependent on various factors, including the order of discovery, sequence analysis, overall structure, and positioning of the motor core. Leaders in the field, in order to minimise the confusion brought about by this seemingly haphazard scheme, standardised the nomenclature in 2004. The individual sequence names remained unchanged, but the family names were all assigned the name “kinesin” and members were grouped into families based on a systematic phylogenetic analysis and, therefore, structural relatedness210 ( see Table 4.1).