The human salivary protein complex (SPC): a large block of related genes.

We have shown that genes for at least six human parotid proteins, parotid acidic protein (Pa), proline-rich protein (Pr), double-banded protein (Db), glycoprotein (Gl), parotid middle-band protein (Pm), and parotid-size variant (Ps) are linked. We have designated this complex of genes as the salivary protein complex (SPC). Several of the genes in this complex show marked associations that are most likely the result of linkage disequilibrium. It seems likely that the SPC arose through the process of gene duplication. This hypothesis is supported by the results of our present study that demonstrate the biochemical similarity of the protein products of several SPC genes. The amino acid compositions of the major SPC proteins are compared, including several (Ps 1 and 2, and Db) that have not been published. All of these proteins are quite similar and consist to a large extent of the amino acids, proline, glycine, and gix (glutamine and/or glutamic acid).