Lowell C A, Potter D A, Stearman R S, Morrow J F
J Biol Chem. 1986 Jun 25;261(18):8442-52.
Serum amyloid A (SAA) is an apolipoprotein produced by the liver in response to inflammation; the levels of SAA mRNA and SAA protein increase at least 500-fold within 24 h. We have obtained clones of all three genes and pseudogene that make up the murine SAA gene family. Two of the genes have 96% sequence homology over their entire length, including introns and flanking sequences 288 base pairs (bp) 5' and 443 bp 3' to the genes: an overall length of 3215 bp. The sharp boundaries between homologous and nonhomologous sequences and the absence of interspersed repeated sequences there suggest that conversion has occurred between these two genes. The homologous regions are bounded by short inverted repeats containing alternating purine and pyrimidine residues, as described for other gene conversion units. The third SAA gene has evolved separately, although all are closely linked on chromosome 7. Comparison of the upstream regions of the SAA genes with those of the rat fibrinogen genes, whose expression is also induced by inflammation, reveals sequences common to all six genes which are very improbable on a random basis.
血清淀粉样蛋白A（SAA）是肝脏在炎症反应时产生的一种载脂蛋白；SAA信使核糖核酸（mRNA）和SAA蛋白的水平在24小时内至少增加500倍。我们已经获得了构成小鼠SAA基因家族的所有三个基因和假基因的克隆。其中两个基因在其全长范围内具有96%的序列同源性，包括内含子以及基因5'端288个碱基对（bp）和3'端443个bp的侧翼序列：全长为3215 bp。同源序列和非同源序列之间的清晰界限以及其间不存在散布的重复序列表明这两个基因之间发生了基因转换。如其他基因转换单位所述，同源区域由包含交替嘌呤和嘧啶残基的短反向重复序列界定。第三个SAA基因是独立进化的，尽管它们在7号染色体上都紧密连锁。将SAA基因的上游区域与大鼠纤维蛋白原基因的上游区域进行比较，大鼠纤维蛋白原基因的表达也受炎症诱导，结果发现所有六个基因共有的序列在随机情况下极不可能出现。
