Unique phylogenetic distributions of the Ska and Dam1 complexes support functional analogy and suggest multiple parallel displacements of Ska by Dam1

Faithful chromosome segregation relies on kinetochores, the large protein complexes that connect chromatin to spindle microtubules. Although human and yeast kinetochores are largely homologous, they track microtubules with the unrelated protein complexes Ska (Ska-C, human) and Dam1 (Dam1-C, yeast). We here uncovered that Ska-C and Dam1-C are both widespread among eukaryotes, but in an exceptionally inversemanner, supporting their functional analogy. Within the complexes, all Ska-C and various Dam1-C subunits are ancient paralogs, showing that gene duplication shaped these complexes.Weexamined various evolutionary scenarios to explain the nearlymutually exclusive patterns of Ska-C andDam1-C in present-day species.Wepropose that Ska-C was present in the last eukaryotic commonancestor, that subsequently Dam1-C displaced Ska-C in an early fungus andwas horizontally transferred to diverse non-fungal lineages, displacing Ska-C in these lineages too.