Full Length Research Paper Molecular Cloning and Characterization of a Novel Human Putative Transmembrane Protein Homologous to Mouse Sideroflexin Associated with Sideroblastic Anemia* HUARUI ZHENG, CHAONENG JI, XIANQIONG ZOU, MAOQING WU, ZHE JIN, GANG YIN, JIXI LI, CONGJING FENG, HAIPENG CHENG, SHAOHUA GU, YI XIE † and YUMIN MAO ‡ State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai 200433, People’s Republic of China (Received 7 May 2003) Sideroflexin1 (Sfxn1), the prototype of a novel family of evolutionarily conserved proteins present in eukaryotes, has been found mutated in mice with siderocytic anemia. It is speculated that this protein facilitates the transport of a component required for iron utilization into mitochon- drial. During the large-scale sequencing analysis of a human fetal brain cDNA library, we isolated a cDNA encoding a novel sideroflexin protein (SFXN4), which showed 59% identity and 71% similarity to mouse sideroflexin4. According to the search of the human genome database, SFXN4 gene is mapped to chromosome 10q25-26 and spans more than 24.7 kb of the genomic DNA. It is 1428 base pair in length and the putative protein contains 305 amino acids with a conserved predicted five-transmembrane-domains structure. RT- PCR result shows that the SFXN4 gene is expressed in many tissues. Keywords: SFXN4; cDNA cloning; Sideroblastic anemia; RT-PCR MAIN TEXT Iron plays an essential role in some basic biological processes such as transport of oxygen and electrons. Excess of iron can promote oxidative damage to vital biological structures. Therefore iron homeostasis should be tightly regulated (Aisen et al., 2001; Roy and Andrews, 2001). One of disorders in iron metabolism is anemia, because of its role in heme synthesis which is associated with mitochondrial metabolism. Virtually all the iron in erythroblasts is imported into the mitochondrial, where it is incorporated into protoporphyin IX to make heme. Deficiency in protoporphyin synthesis would result in mitochondrial iron accumulation, which is the hallmark of sideroblastic anemias (Ponka, 1999; Mesenholler and Matthews, 2000). It has been speculated that enzyme defect in heme synthetic pathway may lead to a shortage of heme precursors, thereby impairing the utilization of iron (Gattermann, 1999) Delta-Aminolevulinic acid synthetase(ALAS2) is the first enzyme of the heme synthetic pathway. Mutations in ALAS2 has been well characterized in association with X-linked sideroblastic anemia (Cox et al., 1994; Harigae et al., 1998; Hurford et al., 2002) and many patients respond to pharmacological dose of pyridoxine, a cofactor for ALAS2 (Manabe et al., 1982; Harris et al., 1993). A recently identified novel gene, sideroflexin1 (Sfxn1), which encodes a mitochondrial membrane protein, has been found mutated in mice with siderocytic anemia (Fleming et al. 2001). Considering the pathogenesis of siderocytic anemia and the struc- tural features of Sfxn1, it is speculated that this protein facilitates the transport of a component required for iron utilization into mitochondrial. As there is an obvious similarity between mice mutated in Sfxn1 and mice deprived of pyridoxine, ISSN 1042-5179 print/ISSN 1029-2365 online q 2003 Taylor & Francis Ltd DOI: 10.1080/10425170310001605491 *The Nucleotide Sequence reported in this paper has been submitted to GenBank under Accession Number AY269785. † Tel.: þ 86-21-55520025. ‡ Corresponding author. Tel.: þ86-21-65643573. Fax: þ86-21-65642502. E-mail: ymmao@fudan.edu.cn DNA Sequence, October 2003 Vol. 14 (5), pp. 369–373