Essential component of the mitotic spindle required for faithful chromosome segregation and progression into anaphase. Promotes the metaphase-to-anaphase transition and is required for chromosome alignment; normal timing of sister chromatid segregation; and maintenance of spindle pole architecture. The astrin (SPAG5)-kinastrin (SKAP) complex promotes stable microtubule-kinetochore attachments. Required for kinetochore oscillations and dynamics of microtubule plus-ends during live cell mitosis; possibly by forming a link between spindle microtubule plus-ends and mitotic chromosomes to achieve faithful cell division. {ECO:0000250|UniProtKB:Q9Y448}.