Abstract
The cDNA probe pSAA82 detects three serum amyloid A (SAA) loci on chromosome 11p. SAA1 and SAA2 have 90% nucleotide identity in exon and intron sequences (1), whereas SAA3 has an average of 70% identity with SAA1 and SAA2 (3). The chromosomal organization of the loci is not yet known. A two-allele polymorphic HindIII site was found within intron 2 of the SAA2 locus (1) with fragments of 3.0 (a2) and 5.0 kb (a1) (previously sized as 2.8 and 4.6 kb, respectively) which occur in Caucasoids, Negroids, and San (formerly [open quote]Bushmen[close quotes]) (2). The discovery of a further, Negroid-specific, polymorphic HindIII restriction site, detected with the same probe, increases its usefulness. This RFLP is associated with the SAA1 locus (6) and is characterized by the presence of two allelic fragments of 3.6 (b1) and 1.4 kb (b2). This HindIII site is also thought to occur within intron 2 because of the strong evolutionary conservation between the SAA1 and SAA2 genes. The polymorphism may therefore either predate the gene duplication event or be present as a result of gene conversion. 6 refs., 1 fig.
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