The major clotting protein from guinea pig seminal vesicle contains eight repeats of a 24-amino acid domain

The complete amino acid sequence of the major clotting protein from the guinea pig seminal vesicle (SVP-1) has been determined by nucleotide sequencing of cDNA clones corresponding to the 3' terminus of an mRNA that codes for a protein precursor to SVP-1. The first 40 amino acids of the derived protein sequence are identical to those determined by N-terminal sequencing of SVP-1 isolated from the lumen of the seminal vesicle. This finding confirms that SVP-1 is cleaved from the C terminus of a larger precursor protein. The portion of the nucleotide sequence that codes for SVP-1 contains eight highly homologous but imperfect repeats of a 72-nucleotide domain. This repeated structure is also evident at the amino acid level. The consensus 24-amino acid repeat unit contains two lysine and three glutamine residues. Since the clotting of SVP-1 is known to involve the formation of γ-glutamyl-ε-lysine crosslinks, it is likely that the 24-amino acid repeating unit is the unit of function of SVP-1.