Identification of a novel serum amyloid a protein in BALB/c mice

Four serum amyloid A protein (SAA) genes and two SAA gene products, SAA₁ and SAA₂, were identified in BALB/c mice. Using analytical isoelectric focusing we have identified a quantitatively significant new member of the SAA family and designated it 'SAA₅'. This protein has characteristics never before described for any SAA molecule. In the highly conserved region between amino acids 33 and 44, identical in all SAAs from all species examined, SAA₅ had four amino acid substitutions. In addition, the induction of SAA₅ by lipopolysaccharide had different kinetics from that of the other mouse SAAs. Our data suggest that the mouse SAA gene family is more complex in composition and regulation than previously surmised.