A novel mRNA of the A4 amyloid precursor gene coding for a possibly secreted protein.

The gene, encoding the A4 peptide found in the amyloid core of senile plaques isolated from the cerebral cortex of patients with Alzheimer's disease, produces at least three precursors that resemble cell surface receptors. A clone isolated from a human brain complementary DNA library contained the structural sequence for an A4 amyloid peptide precursor with a serine protease inhibitor domain in which 208 amino acids at the carboxyl terminal are replaced by 20 amino acids derived from nucleotide sequences with homology to the Alu repeat family. This protein devoid of the transmembrane domain most likely represents a secreted form of the A4 amyloid peptide precursor.