Vaccinia virus proteins A36 and F12/E2 show strong preferences for different kinesin light chain isoforms

Vaccinia virus (VACV) utilizes microtubule‐mediated trafficking at several stages of its life cycle, of which virus egress is the most intensely studied. During egress VACV proteins A36, F12 and E2 are involved in kinesin‐1 interactions; however, the roles of these proteins remain poorly understood. A36 forms a direct link between virions and kinesin‐1, yet in its absence VACV egress still occurs on microtubules. During a co‐immunoprecipitation screen to seek an alternative link between virions and kinesin, A36 was found to bind isoform KLC1 rather than KLC2. The F12/E2 complex associates preferentially with the C‐terminal tail of KLC2, to a region that overlaps the binding site of cellular 14‐3‐3 proteins. F12/E2 displaces 14‐3‐3 from KLC and, unlike 14‐3‐3, does not require phosphorylation of KLC for its binding. The region determining the KLC1 specificity of A36 was mapped to the KLC N‐terminal heptad repeat region that is responsible for its association with kinesin heavy chain. Despite these differing binding properties F12/E2 can co‐operatively enhance A36 association with KLC, particularly when using a KLC1‐KLC2 chimaera that resembles several KLC1 spliceforms and can bind A36 and F12/E2 efficiently. This is the first example of a pathogen encoding multiple proteins that co‐operatively associate with kinesin‐1.