This family consists of several mammalian dentin matrix protein 1 (DMP1) sequences. The dentin matrix acidic phosphoprotein 1 (DMP1) gene has been mapped to human chromosome 4q21. DMP1 is a bone and teeth specific protein initially identified from mineralized dentin. DMP1 is primarily localized in the nuclear compartment of undifferentiated osteoblasts. In the nucleus, DMP1 acts as a transcriptional component for activation of osteoblast-specific genes like osteocalcin. During the early phase of osteoblast maturation, Ca(2+) surges into the nucleus from the cytoplasm, triggering the phosphorylation of DMP1 by a nuclear isoform of casein kinase II. This phosphorylated DMP1 is then exported out into the extracellular matrix, where it regulates nucleation of hydroxyapatite. DMP1 is a unique molecule that initiates osteoblast differentiation by transcription in the nucleus and orchestrates mineralized matrix formation extracellularly, at later stages of osteoblast maturation. The DMP1 gene has been found to be ectopically expressed in lung cancer although the reason for this is unknown.