Cloning and characterization of the gene encoding human osteoprotegerin/osteoclastogenesis-inhibitory factor

The human osteoprotegerin (OPG)-osteoclastogenesis-inhibitory factor (OCIF) gene has been cloned and characterized. The OPG-OCIF gene is a single-copy gene consisting of five exons, and spans 29 kb of the human genome. All the exon/intron boundaries comply with the GT/AG rule. The translation-termination codon is present in exon 5 and a typical poly(A)-addition signal resides 173-nucleotides downstream of the translation-termination codon. A major transcription-initiation site is present 67-nucleotides upstream of the initiation ATG codon. Two minor sites are present further upstream. The 4.2-kb and 6.5-kb transcripts detected in IMR-90 cells were found to contain the 3'-half of intron 2 and the entire intron 2, respectively. In the OPG-OCIF gene, a single intron divides the stretch that encode four Cys-rich motifs, implying diversity from the other members of the tumor necrosis factor receptor (TNFR) family. Two death domain homologous regions (DDHs) present in tandem in OPG-OCIF are encoded separately by exons 4 and 5. The conservation of amino-acid sequences suggests that exon 4 is produced by a duplication of a portion of exon 5.