CLONING AND IDENTIFICATION OF HEM14, THE YEAST GENE FOR MITOCHONDRIALPROTOPORPHYRINOGEN OXIDASE

A respiratory-defective mutant (C54) of Saccharomyces cerevisiae was f ound to have a phenotype consistent with a mutation in either mitochon drial protoporphyrinogen oxidase or ferrochelatase. The mutant is gros sly deficient in hemes, accumulates protoporphyrin and is rescued by e xogenous heme. The increased levels of protoporphyrin at the expense o f heme is indicative of a block in one of the two last steps of the he me biosynthetic pathway. Complementation of C54 by a known ferrochelat ase mutant suggested that the defect was most likely in HEM14 encoding protoporphyrinogen oxidase. A plasmid capable of complementing C54 wa s obtained by transformation with a yeast genomic plasmid library. A p artial sequence of the insert identified the gene as reading frame YER 014 of yeast chromosome V (GenBank Accession Number U18778). This read ing frame codes for a protein homologous to human protoporphyrinogen o xidase. Disruption of this gene elicits a respiratory defect and accum ulation of protoporphyrin. The phenotype of the null mutant together w ith the homology of YER014p to human protoporphyrinogen oxidase provid e compelling evidence that YER014 is HEM14.