THE 5TH SERUM AMYLOID-A-RELATED GENE SEQUENCE, GSAA4, IS SAA3

The human serum amyloid A (SAA) gene family consists of two acute phas e genes, SAA1 and SAA2; a pseudogene, SAA3 and a fourth gene, SAA4. Th e existence of SAA4 was first described in this laboratory. Subsequent ly, Sack and Talbot isolated a clone, designated GSAA4, which had homo logy to SAA3. The clone was described as the same as SAA4 and was char acterized as a pseudogene. However, our restriction site and sequence analyses of SAA4 demonstrated that SAA4 and GSAA4 are separate entitie s. SAA4 encodes a functional, constitutively expressed protein. Recent ly, the GSAA4 clone has been reported by Sellar and Whitehead as const ituting a fifth SAA-related sequence. However, we have demonstrated th at GSAA4 has striking homology with the 3' terminus of SAA3 in the rev erse orientation. Furthermore, computer analyses strongly indicate tha t 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 s equence of the 3' region of SAA3. The SAA family must therefore still be viewed as consisting of four SAA loci at present.