Myosin phosphatase target subunit 1 (MYPT1), which is also called the myosin-binding subunit of myosin phosphatase, is one of the subunits of myosin phosphatase. Myosin phosphatase regulates the interaction of actin and myosin downstream of the guanosine triphosphatase Rho, as previously shown (K. Kimura, et al., 1996, Science 273:245-248). To understand the role of MYPT1 in the regulation of the cytoskeleton in human diseases, we have cloned a 4855-bp cDNA for human MYPT1 using the rat MYPT1 cDNA as probe. Sequencing analysis has revealed that human MYPT1 contains 1030 amino acid residues with a calculated molecular mass of approximately 115 kDa. Fluorescence in situ hybridization analysis placed the human MYPT1 gene on chromosome 12q15-q21.2. Radiation hybrid mapping has shown that the human MYPT1 gene is located very near the highly polymorphic marker CHLC.GATA65A12, which lies between D12S350 and D12S106.