RESUMO
The replication and repair of organellar genomes in the malaria parasite Plasmodium falciparum is poorly understood. We have assessed the properties of an open reading frame Pfprex (formerly known as pom1) and confirm that it specifies a multi-domain polypeptide with DNA primase, DNA helicase, DNA polymerase and 3'-5' exonuclease activities. The sequence of the primase/helicase domain is phylogenetically related to the T7-bacteriophage gene 4 product and mammalian mitochondrial helicase, Twinkle. Despite that, the N-terminal sequence of this multi-domain polypeptide directs a green fluorescent protein reporter specifically to the P. falciparum apicoplast and not to the mitochondrion. Phylogenetic analysis placed the DNA polymerase sequence with the family A bacterial polymerases, most closely to those of the thermophilic Aquifex species. Notably, the malarial enzyme was optimally active at 75 degrees C. Pfprex is the first example of a gene encoding contiguous DNA polymerase, DNA primase and DNA helicase components. We propose it has a key role in replication of the malarial plastid genome, a validated drug target.
Assuntos
Replicação do DNA , Complexos Multienzimáticos/genética , Organelas/metabolismo , Plasmodium falciparum/enzimologia , Proteínas de Protozoários/genética , Animais , DNA Helicases/química , DNA Helicases/genética , DNA Helicases/metabolismo , DNA Polimerase III/química , DNA Polimerase III/genética , DNA Polimerase III/metabolismo , DNA Primase/química , DNA Primase/genética , DNA Primase/metabolismo , Exonucleases/química , Exonucleases/genética , Exonucleases/metabolismo , Genes de Protozoários , Genes Reporter , Proteínas de Fluorescência Verde/análise , Proteínas de Fluorescência Verde/genética , Complexos Multienzimáticos/química , Complexos Multienzimáticos/metabolismo , Organelas/genética , Filogenia , Plasmodium falciparum/genética , Estrutura Terciária de Proteína , Transporte Proteico , Proteínas de Protozoários/química , Proteínas de Protozoários/metabolismo , Homologia de SequênciaRESUMO
Plasmodium berghei and Plasmodium chabaudi are widely used model malaria species. Comparison of their genomes, integrated with proteomic and microarray data, with the genomes of Plasmodium falciparum and Plasmodium yoelii revealed a conserved core of 4500 Plasmodium genes in the central regions of the 14 chromosomes and highlighted genes evolving rapidly because of stage-specific selective pressures. Four strategies for gene expression are apparent during the parasites' life cycle: (i) housekeeping; (ii) host-related; (iii) strategy-specific related to invasion, asexual replication, and sexual development; and (iv) stage-specific. We observed posttranscriptional gene silencing through translational repression of messenger RNA during sexual development, and a 47-base 3' untranslated region motif is implicated in this process.
Assuntos
Genoma de Protozoário , Estágios do Ciclo de Vida , Plasmodium/crescimento & desenvolvimento , Plasmodium/genética , Proteoma/análise , Regiões 3' não Traduzidas , Animais , Anopheles/parasitologia , Biologia Computacional , Evolução Molecular , Perfilação da Expressão Gênica , Inativação Gênica , Genes de Protozoários , Malária/parasitologia , Análise de Sequência com Séries de Oligonucleotídeos , Plasmodium/metabolismo , Plasmodium berghei/genética , Plasmodium berghei/crescimento & desenvolvimento , Plasmodium berghei/metabolismo , Plasmodium chabaudi/genética , Plasmodium chabaudi/crescimento & desenvolvimento , Plasmodium chabaudi/metabolismo , Plasmodium falciparum/genética , Plasmodium falciparum/crescimento & desenvolvimento , Plasmodium falciparum/metabolismo , Plasmodium yoelii/genética , Plasmodium yoelii/crescimento & desenvolvimento , Plasmodium yoelii/metabolismo , Proteômica , Proteínas de Protozoários/análise , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA de Protozoário/genética , RNA de Protozoário/metabolismo , Seleção Genética , Transcrição GênicaRESUMO
Functionally related homologues of known genes can be difficult to identify in divergent species. In this paper, we show how multi-character analysis can be used to elucidate the relationships among divergent members of gene superfamilies. We used probabilistic modelling in conjunction with protein structural predictions and gene-structure analyses on a whole-genome scale to find gene homologies that are missed by conventional similarity-search strategies and identified a variant gene superfamily in six species of malaria (Plasmodium interspersed repeats, pir). The superfamily includes rif in P.falciparum, vir in P.vivax, a novel family kir in P.knowlesi and the cir/bir/yir family in three rodent malarias. Our data indicate that this is the major multi-gene family in malaria parasites. Protein localization of products from pir members to the infected erythrocyte membrane in the rodent malaria parasite P.chabaudi, demonstrates phenotypic similarity to the products of pir in other malaria species. The results give critical insight into the evolutionary adaptation of malaria parasites to their host and provide important data for comparative immunology between malaria parasites obtained from laboratory models and their human counterparts.
Assuntos
Família Multigênica , Plasmodium/genética , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Sequência Conservada , Evolução Molecular , Genes de Protozoários , Genômica , Humanos , Sequências Repetitivas Dispersas , Malária/parasitologia , Filogenia , Proteínas de Protozoários/análise , Proteínas de Protozoários/química , Proteínas de Protozoários/genéticaRESUMO
A major mechanism whereby malaria parasites evade the host immune response to give chronic infections in patients' blood for months, or even years, is antigenic variation. In order to generate variant antigens, parasites require large multigene families. Although several gene families involved in these phenomena have been identified in the human malaria Plasmodium falciparum, to date no variant antigen gene families have been identified in malaria species that will infect widely used rodent laboratory hosts. Here we present, for the first time, to our knowledge, a large multigene family conserved in both rodent and human malarias, which is a strong candidate as a major variant antigen gene family. In each of four species of Plasmodium, three rodent malarias and the human pathogen P. vivax, homologues of the gene family were found to have a conserved three-exon structure. In the rodent malaria P. chabaudi, transcription of members of the gene family was developmentally regulated with maximum expression in late trophozoite stages, which is the developmental stage known to express variant antigen proteins.
