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Eukaryotic Cell, December 2005, p. 2087-2097, Vol. 4, No. 12
1535-9778/05/$08.00+0     doi:10.1128/EC.4.12.2087-2097.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Enzymes of the Heme Biosynthetic Pathway in the Nonphotosynthetic Alga Polytomella sp.{dagger}

Ariane Atteia,{ddagger} Robert van Lis,{ddagger} and Samuel I. Beale*

Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912

Received 10 August 2005/ Accepted 25 September 2005

Heme biosynthesis involves a number of enzymatic steps which in eukaryotes take place in different cell compartments. Enzyme compartmentalization differs between photosynthetic and nonphotosynthetic eukaryotes. Here we investigated the structures and subcellular localizations of three enzymes involved in the heme pathway in Polytomella sp., a colorless alga evolutionarily related to the green alga Chlamydomonas reinhardtii. Functional complementation of Escherichia coli mutant strains was used to isolate cDNAs encoding three heme biosynthetic enzymes, glutamate-1-semialdehyde aminotransferase, protoporphyrinogen IX oxidase, and ferrochelatase. All three proteins show highest similarity to their counterparts in photosynthetic organisms, including C. reinhardtii. All three proteins have N-terminal extensions suggestive of intracellular targeting, and immunoblot studies indicate their enrichment in a dense cell fraction that is enriched in amyloplasts. These results suggest that even though the plastids of Polytomella sp. are not photosynthetically active, they are the major site of heme biosynthesis. The presence of a gene for glutamate-1-semialdehyde aminotransferase suggests that Polytomella sp. uses the five-carbon pathway for synthesis of the heme precursor 5-aminolevulinic acid.

* Corresponding author. Mailing address: Division of Biology and Medicine, Brown University, Providence, RI 02912. Phone: (401) 863-3129. Fax: (401) 863-1182. E-mail: sib{at}brown.edu.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

{ddagger} Present address: Physiologie Cellulaire Végétale, UMR5168 CEA Grenoble, 17 rue des Martyrs, Grenoble cedex 9, 38054, France.

Eukaryotic Cell, December 2005, p. 2087-2097, Vol. 4, No. 12
1535-9778/05/$08.00+0     doi:10.1128/EC.4.12.2087-2097.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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