The fifth serum amyloid A-related gene sequence, GSAA4, is SAA3

The human serum amyloid A (SAA) gene family consists of two acute phase genes, SAA1 and SAA2; a pseudogene, SAA3 and a fourth gene, SAA4. The existence of SAA4 was first described in this laboratory. Subsequently, Sack & Talbot isolated a clone, designated GSAA4, which had homology to SAA3. The clone was described as the same as SAA4 and was characterized as a pseudogene. However, our restriction site and sequence analyses of SAA4 demonstrated that SAA4 and GSAA4 are separate entities. SAA4 encodes a functional, constitutively expressed protein. Recently, the GSAA4 clone has been reported by Sellar & Whitehead as constituting a fifth SAA-related sequence. However, we have demonstrated that GSAA4 has striking homology with the 3' terminus of SAA3 in the reverse orientation. Furthermore, computer analyses strongly indicate that the GSAA4 or fifth SAA-related sequence is in fact, a clone from the SAA3 locus. We have amplified, isolated and sequenced fragments from genomic DNA which demonstrate that the GSAA4 sequence is the correct sequence of the 3' region of SAA3. The SAA family must therefore still be viewed as consisting of four SAA loci at present.