A gene product of the mouse t complex with chemical properties of a cell surface-associated component of the extracellular matrix

p63/6.9 is a major testicular cell protein coded for by a gene, called Tcp-1, within the mouse t complex. All wild-type chromosomes carry the Tcp-1^b allele which codes for a basic form of this protein, while all complete mutant t haplotypes carry the Tcp-1^a allele which codes for an acidic form of this protein. Genetic studies have demonstrated a correlation between the Tcp-1 gene and certain t haplotype effects on sperm differentiation and maturation. In this report, an initial biochemical analysis of the p63/6.9 protein is presented. The data provide evidence that p63/6.9 is closely associated with the external surface of testicular cells but not as an integral membrane component. Some properties of the testicular form of this t complex gene product are similar to those reported for the matrix proteins fibronectin and laminin. The possibility is suggested that primary effects of t haplotypes on sperm differentiation could be exerted through the extracellular matrix. p63/6.9 is also present at a lower level within the cytoplasm and membranes of F9 teratocarcinoma cells. It appears that the level of p63/6.9 synthesis and the exact nature of p63/6.9 intra- and/or intermolecular interactions are under tissue-specific control.