Molecular cloning of the cDNA coding for proline-rich protein (PRP): identity of PRP as C4b-binding protein.

Proline-rich protein (PRP) is a plasma protein with a high proportion of proline residues and possessing lipid-binding properties. In order to clarify its structure, a human liver cDNA library was screened using anti-PRP antiserum. Several overlapping phage cDNA clones were isolated and the total nucleotide sequence of the cDNA, 2178 bp in length, was analyzed. The amino acid composition of PRP deduced from the cDNA was essentially the same as that reported for PRP. In a homology search, the cDNA sequence was almost completely the same as the previously reported cDNA sequence of C4b-binding protein. Furthermore, the reported molecular weights of the two proteins under both reduced and unreduced conditions were quite alike. These findings indicate that PRP is identical with C4bp.