MARK4 contains an N-terminal serine/threonine kinase domain, a central ubiquitin-associated domain, and a C-terminal KA1-associated kinase domain. RT-PCR analysis detects upregulated expression of the gene for MARK4 in nearly all clinical hepatocellular carcinoma cells. Northern blot analysis reveals ubiquitous expression of a 3.6-kb transcript, with highest expression in testis. Immunofluorescence microscopy demonstrates homogeneous cytoplasmic expression. Colony-forming assays show that MARK4 antisense reduces the growth of SNU475 cells. It has been suggested that MARK4 provides a growth advantage to cells.