Hoskins J, Norman D K, Beckmann R J, Long G L
Proc Natl Acad Sci U S A. 1987 Jan;84(2):349-53. doi: 10.1073/pnas.84.2.349.
Human liver cDNA encoding a protein S precursor was isolated from two cDNA libraries by two different techniques. Based upon the frequency of positive clones, the abundance of mRNA for protein S is approximately 0.01%. Blot hybridization of electrophoretically fractionated poly(A)+ RNA revealed a major mRNA approximately 4 kilobases long and two minor forms of approximately 3.1 and approximately equal to 2.6 kilobases. One of the cDNA clones contains a segment encoding a 676 amino acid protein S precursor, as well as 108 and 1132 nucleotides of 5' and 3' noncoding sequence, respectively, plus a poly(A) region at the 3' end. The cDNAs are adenosine plus thymidine-rich (60%) except for the 5' noncoding region, where 78% of the nucleotides are guanosine or cytosine. The protein precursor consists of a 41 amino acid "leader" peptide followed by 635 amino acids corresponding to mature protein S. Comparison of the mature protein region with homologous vitamin K-dependent plasma proteins shows that it is composed of the following domains: an amino-terminal gamma-carboxyglutamic acid-rich region of 37 amino acids; a 36 amino acid linker region rich in hydroxy amino acids; four epidermal growth factor-like segments, each approximately 45 amino acids long; and a 387 amino acid carboxyl-terminal domain of unrecognized structure and unknown function.
采用两种不同技术从两个互补DNA文库中分离出编码蛋白S前体的人肝脏互补DNA。根据阳性克隆的频率，蛋白S的信使核糖核酸丰度约为0.01%。对经电泳分离的聚腺苷酸加RNA进行印迹杂交，结果显示一条约4千碱基长的主要信使核糖核酸以及两条约3.1千碱基和约2.6千碱基的次要形式。其中一个互补DNA克隆包含一段编码676个氨基酸的蛋白S前体的序列，以及分别位于5'和3'非编码序列的108和1132个核苷酸，外加3'端的一个聚腺苷酸区域。除5'非编码区域外，互补DNA富含腺苷加胸腺嘧啶（60%），该区域78%的核苷酸为鸟苷或胞嘧啶。蛋白前体由一个41个氨基酸的“前导”肽段和635个对应成熟蛋白S的氨基酸组成。将成熟蛋白区域与同源维生素K依赖血浆蛋白进行比较，结果表明它由以下结构域组成：一个37个氨基酸的富含γ-羧基谷氨酸的氨基末端区域；一个富含羟基氨基酸的36个氨基酸的连接区域；四个表皮生长因子样片段，每个片段约45个氨基酸长；以及一个387个氨基酸的羧基末端结构域，其结构未知且功能不明。
