The Human Acute‐Phase Serum Amyloid A Gene Family: Structure, Evolution and Expression in Hepatoma Cells

Serum amyloid A (SAA) proteins are a group of phylogenetically conserved acute‐phase reactants. Evidence is presented here for the existence of four genetic loci for the human serum amyloid A (SAA) genes. The first locus was defined by three contiguous γ clones spanning =: 30 kb which contained a single SAA gene encoding apoSAA1β. Allelic variants were isolated at (he second locus: a novel clone encoding apoSAA2α was distinguished from SAA2β (previously known as SAAg9, Ref. 1) by a His/Arg polymorphism at residue 71. SAA 1 and SAA2 found in the high density lipoprotein fraction of acute‐phase plasma were =90% homologous at the nucleotide level. Homology in the 5’flanking regions was reflected functionally with similar transcriptional responses to inflammatory cytokines in transfected hepatoma cells. A further novel gene, SAA4. was isolated from a cosmid library and mapped 10 kb downstream of SAA2. The locus defining SAA3 has been described elsewhere [2]. Polymorphisms were detected at both SAA1 and SAA2 loci by Southern analysis and the entire SAA region mapped to discrete fragments by pulsed field analysis. The four genes account for all the hybridizing bands present on Southern analyses in a Caucasian population.