Glasser S W, Korfhagen T R, Perme C M, Pilot-Matias T J, Kister S E, Whitsett J A
Division of Pulmonary Biology, Children's Hospital, Cincinnati, Ohio 45267-0541.
J Biol Chem. 1988 Jul 25;263(21):10326-31.
Human pulmonary surfactant proteolipid of Mr = 5,000, now termed surfactant protein C (SP-C), is produced by proteolytic processing of an Mr = 22,000 precursor. The active hydrophobic peptide imparts surface active properties to pulmonary surfactant phospholipids. We have determined the entire nucleotide sequence of two distinct genes encoding SP-C from a genomic library prepared from human leukocytes. SP-C genes were encoded by approximately 3.0 kilobase pairs of DNA containing six exons and five introns. In both genes, the active hydrophobic region of the polypeptide was located in the second exon that encodes a peptide of 53 amino acids. The entire nucleotide sequences of the two classes of SP-C genes differed by only 1%. Two cDNAs encoding SP-C were distinguished on the basis of an 18-nucleotide deletion at the beginning of the fifth exon; no such deletion was detected within the two classes of SP-C genes. Comparison of the 3'-untranslated regions of SP-C cDNA clones and the two classes of genomic clones demonstrated that cDNAs with and without the 18-base pair deletion could be derived from both of the genes. This 18-base pair deletion occurs in nucleotide sequences compatible with two distinct RNA splice sites. One additional cDNA clone showed the addition of an 8-base pair insert at the end of exon 5, which was also compatible with two distinct splice sites. Both classes of SP-C genes were represented by cDNAs, demonstrating that both classes of genes are actively transcribed. The two SP-C genes were readily distinguished on the basis of their nucleotide sequences and restriction fragment analyses of their flanking DNA. Two distinct classes of human SP-C genes are transcribed, and the heterogeneity in the SP-C RNAs appears to result from differential splicing.
分子量为5000的人肺表面活性物质蛋白脂质，现称为表面活性物质蛋白C（SP-C），是由分子量为22000的前体经蛋白水解加工产生的。活性疏水肽赋予肺表面活性物质磷脂表面活性特性。我们从人白细胞制备的基因组文库中确定了编码SP-C的两个不同基因的完整核苷酸序列。SP-C基因由约3.0千碱基对的DNA编码，包含六个外显子和五个内含子。在这两个基因中，多肽的活性疏水区域位于第二个外显子中，该外显子编码一个53个氨基酸的肽段。这两类SP-C基因的完整核苷酸序列仅相差1%。根据第五个外显子起始处18个核苷酸的缺失，区分了两个编码SP-C的cDNA；在这两类SP-C基因中未检测到这种缺失。对SP-C cDNA克隆和两类基因组克隆的3'非翻译区进行比较表明，有和没有18碱基对缺失的cDNA都可以来自这两个基因。这种18碱基对的缺失发生在与两个不同RNA剪接位点相容的核苷酸序列中。另一个cDNA克隆显示在第5外显子末端添加了一个8碱基对的插入片段，这也与两个不同的剪接位点相容。两类SP-C基因都有相应的cDNA代表，表明这两类基因都在活跃转录。根据它们的核苷酸序列和侧翼DNA的限制性片段分析，很容易区分这两个SP-C基因。人类有两类不同的SP-C基因被转录，SP-C RNA的异质性似乎是由差异剪接导致的。
