Steinkasserer, Alexander; Weiss, Elisabeth H.; Schwaeble, Wilhelm; Linke, Reinhold P.
Heterogeneity of human serum amyloid A protein Five different variants from one individual demonstrated by cDNA sequence analysis.
In: Biochemical Journal, Vol. 268: pp. 187-193
Serum amyloid A (SAA), a chemically polymorphic protein, is the most sensitive marker protein of the acute phase and
the precursor of reactive amyloidosis, which is characterized by deposits of amyloid A protein (AA). We investigated the
variability of the SAA gene family in one individual by sequencing 11 SAA-specific clones from an acute-phase-liver
cDNA library. At least five different SAA variants were deduced from six different cDNAs. The 3' untranslated gene
segments fall into two groups, based on nucleotide sequence and variability in length. Various nucleotide and amino acid
substitutions were found predominantly in the 3' portion. Some of these substitutions are unique and increase the number
of SAA variants in one individual to at least five. Moreover, genomic DNA of four individuals was examined by analysis
of restriction-fragment length polymorphism. Besides two conserved strongly labelled bands, additional polymorphic
bands were observed, indicating isotypic and/or allotypic SAA variations. Finally, three different mRNA species were
detected by Northern-blot analysis, a finding that might be of relevance for the stability of SAA transcripts.