Nakahashi Y, Fujita H, Taketani S, Ishida N, Kappas A, Sassa S
Department of Hygiene, Kansai Medical University, Osaka, Japan.
Proc Natl Acad Sci U S A. 1992 Jan 1;89(1):281-5. doi: 10.1073/pnas.89.1.281.
The molecular basis of an inherited defect of ferrochelatase in a patient with erythropoietic protoporphyria (EPP) was investigated. Ferrochelatase is the terminal enzyme in the heme biosynthetic pathway and catalyzes the insertion of ferrous iron into protoporphyrin IX to form heme. In Epstein-Barr virus-transformed lymphoblastoid cells from a proband with EPP, enzyme activity, an immunochemically quantifiable protein, and mRNA content of ferrochelatase were about one-half the normal level. In contrast, the rate of transcription of ferrochelatase mRNA in the proband's cells was normal, suggesting that decreased ferrochelatase mRNA is due to an unstable transcript. cDNA clones encoding ferrochelatase in the proband, isolated by amplification using the polymerase chain reaction, were found to be classified either into those encoding the normal protein or into those encoding an abnormal protein that lacked exon 2 of the ferrochelatase gene, indicating that the proband is heterozygous for the ferrochelatase defect. Genomic DNA analysis revealed that the abnormal allele had a point mutation, C----T, near the acceptor site of intron 1. This point mutation appears to be responsible for the post-transcriptional splicing abnormality resulting in an aberrant transcript of ferrochelatase in this patient.
对一名红细胞生成性原卟啉症（EPP）患者体内亚铁螯合酶遗传性缺陷的分子基础进行了研究。亚铁螯合酶是血红素生物合成途径中的末端酶，催化亚铁离子插入原卟啉IX中以形成血红素。在来自一名EPP先证者的爱泼斯坦-巴尔病毒转化的淋巴母细胞中，亚铁螯合酶的酶活性、免疫化学可定量的蛋白质以及mRNA含量约为正常水平的一半。相比之下，先证者细胞中亚铁螯合酶mRNA的转录速率正常，这表明亚铁螯合酶mRNA减少是由于转录本不稳定所致。通过聚合酶链反应扩增分离出的先证者中编码亚铁螯合酶的cDNA克隆，发现其可分为编码正常蛋白质的克隆和编码缺乏亚铁螯合酶基因外显子2的异常蛋白质的克隆，这表明先证者为亚铁螯合酶缺陷的杂合子。基因组DNA分析显示，异常等位基因在第1内含子的受体位点附近有一个点突变，C→T。该点突变似乎导致了转录后剪接异常，从而在该患者中产生了异常的亚铁螯合酶转录本。
