We isolated and sequenced a cDNA encoding bovine bone sialoprotein (BSP) using a bovine cDNA library made from mRNA isolated from bone-derived cell cultures and ligated to a phage lambda gt11. One of the cDNA clones isolated from this library had a 1800 base pair long insert and was found to contain the entire protein-encoding region. The deduced protein sequence revealed a 310 amino acid protein containing a signal peptide sequence of 16 hydrophobic amino acids. The protein sequence shows remarkable conservation with previously published human and rat sequences (more than 80% similarity for both species). The potential functional domains of BSP, including three acid amino acid-rich sequences, tyrosine sulfation consensus repeats, and the RGD cell binding sequence, are all present in the bovine sequence. Northern analysis of RNA from different bovine tissues indicated the presence of BSP message in bone but not in other nonmineralized tissues, confirming that bone is the major site of BSP message production.