title: The Toxoplasma gondii plastid replication and repair enzyme complex, PREX.
abstract: A plastid-like organelle, the apicoplast, is essential to the majority of medically and veterinary important apicomplexan protozoa including Toxoplasma gondii and Plasmodium. The apicoplast contains multiple copies of a 35 kb genome, the replication of which is dependent upon nuclear-encoded proteins that are imported into the organelle. In P. falciparum an unusual multi-functional gene, pfprex, was previously identified and inferred to encode a protein with DNA primase, DNA helicase and DNA polymerase activities. Herein, we report the presence of a prex orthologue in T. gondii. The protein is predicted to have a bi-partite apicoplast targeting sequence similar to that demonstrated on the PfPREX polypeptide, capable of delivering marker proteins to the apicoplast. Unlike the P. falciparum gene that is devoid of introns, the T. gondii prex gene carries 19 introns, which are spliced to produce a contiguous mRNA. Bacterial expression of the polymerase domain reveals the protein to be active. Consistent with the reported absence of a plastid in Cryptosporidium species, in silico analysis of their genomes failed to demonstrate an orthologue of prex. These studies indicate that prex is conserved across the plastid-bearing apicomplexans and may play an important role in the replication of the plastid genome.
authors.affiliation: Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8TA, UK.
authors.forename: A
authors.initials: A
authors.lastname: Mukhopadhyay
authors.forename: C-Y
authors.initials: CY
authors.lastname: Chen
authors.forename: C
authors.initials: C
authors.lastname: Doerig
authors.forename: F L
authors.initials: FL
authors.lastname: Henriquez
authors.forename: C W
authors.initials: CW
authors.lastname: Roberts
authors.forename: M P
authors.initials: MP
authors.lastname: Barrett
mesh_terms: D000818:Animals; D004265:DNA Helicases / Q000235:genetics; D019915:DNA Primase / Q000235:genetics; D004261:DNA Replication; D016054:DNA, Protozoan / Q000235:genetics / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D005091:Exons / Q000235:genetics; D018503:Genome, Protozoan; D007438:Introns / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014122:Toxoplasma / Q000201:enzymology* / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure
chemical_list: D016054:DNA, Protozoan; D009097:Multienzyme Complexes; D015800:Protozoan Proteins; D019915:DNA Primase; D004259:DNA-Directed DNA Polymerase; D004265:DNA Helicases