The human protoporphyrinogen oxidase gene (PPOX): organization and location to chromosome 1

We determined the structure of the human protoporphyrinogen oxidase (PPOX) gene after isolation and characterization of lambda phage clones mapping discrete regions of the cDNA. Southern blotting of human genomic DNA showed that there is a single copy of the PPOX gene, and fluorescence in situ hybridization to metaphase chromosomes mapped the gene to region 1q22. The gene has 13 exons and about 8 kb. The exon/intron boundary sequences conform to consensus acceptor (GTn) and donor (nAG) sequences, and exons in the gene appear to encode functional protein domains. Primer extension analysis revealed two major transcriptional initiation sites in a region with sequence motifs characteristic of a promoter. The promoter region contains multiple Sp1 elements, CCAAT boxes, and potential GATA-1 binding sites. Mapping of the 5' end PPOX mRNA by polymerase chain reaction indicated that there are the same transcripts in erythroid and nonerythroid cells.