The microtubule matrix within a cell plays a central role in intracellular transport, cell shape during differentiation and chromosome partitioning during mitosis. During these processes, microtubules transition rapidly between stable and dynamic states. MAP/microtubule affinity-regulating kinase 1 (MARK1) is a 795 amino acid protein belonging to the CAMK Ser/Thr protein kinase family. MARK1 is thought to play a role in the stability of the microtubule matrix of the cytoskeleton. MARK1 is activated by phosphorylation of Thr215 by LKB1 in complex with STRAD and MO25. Localized to the cytoskeleton, MARK1 contains one kinase-associated (KA1) domain, one protein kinase domain and one UBA domain. Expressed as three isoforms produced by alternative splicing, MARK1 is found with highest levels in brain, skeletal muscle and heart.