RESUMO
Astasia longa is a colourless heterotrophic flagellate closely related to the photoautotrophic Euglena gracilis. A circular 73 kb plastid DNA (ptDNA) has been isolated from A. longa that is about half the size of the chloroplast DNA of E. gracilis (143 kb). We have determined the complete sequence of the ptDNA of A. longa and established a complete gene map. All chloroplast genes for photosynthesis-related proteins are completely absent from the A. longa plastid DNA except for rbcL, the gene for the ribulose-1,5-bisphosphate carboxylase large subunit. Identified genes encode components of the plastid transcriptional and translational machinery: genes for three subunits of a chloroplast RNA polymerase, 20 chloroplast ribosomal protein genes, a gene for a plastid elongation factor Tu, 27 plastidic tRNA genes and three tandemly arranged repeats of 16S, 23S and 5S rDNA. Transcripts of a number of genes were detected by Northern hybridisation. The ribulose-1,5-bisphosphate carboxylase large subunit protein has been identified by immunoblotting.
Assuntos
Euglênidos/genética , Eucariotos/genética , Plastídeos/genética , Animais , Mapeamento Cromossômico , Genoma , Íntrons , Dados de Sequência Molecular , Família Multigênica , RNA Ribossômico 16SRESUMO
The colourless, nonphotosynthetic protist Astasia longa is phylogenetically related to Euglena gracilis. The 73-kb plastid DNA (ptDNA) of A. longa is about half the size of most chloroplast DNAs (cpDNAs). More than 38 kb of the Astasia ptDNA sequence has been determined. No genes for photosynthetic function have been found except for rbcL. Identified genes include rpoB, tufA, and genes coding for three rRNAs, 17 tRNAs, and 13 ribosomal proteins. Not only is the nucleotide sequence of these genes highly conserved between A. longa and E. gracilis, but a number of these genes are clustered in a similar fashion and have introns in the same positions in both species. The results further support the idea that photosynthetic genes normally encoded in cpDNA have been preferentially lost in Astasia, but that the chloroplast genes coding for components of the plastid translational apparatus have been maintained. This apparatus might be needed for the expression of rbcL and also for that of still unidentified nonphotosynthetic genes of Astasia ptDNA.
Assuntos
Cloroplastos/metabolismo , DNA de Cloroplastos , Eucariotos/genética , Genes de Protozoários/genética , Animais , DNA de Cloroplastos/fisiologia , DNA de Protozoário , Dados de Sequência Molecular , Fases de Leitura Aberta , Biossíntese de Proteínas , Proteínas de Protozoários/genética , RNA Ribossômico/genética , RNA de Transferência/genética , Proteínas Ribossômicas/genéticaRESUMO
Present methods for assessment of the attack phase of malaria eradication are inadequate, particularly lacking any objective parasitological criteria of success. The most objective of the criteria used has been the absence of infections among infants. This has always been subject to the drawback that it is rarely possible to get enough infants to secure a statistically reliable result. Moreover, all the variants used have been subject to the difficulty that it is impossible to prove a total negative without examination of the entire population, and there has always been uncertainty on the scale of examination which was required for adequacy. The authors have therefore undertaken a careful review of parasitological criteria for the interruption of transmission, with the intention of producing precise and objective criteria from which clear-cut conclusions could be reached on the adequacy of the attack mechanism. In theory the total interruption of transmission should produce readily foreseeable results in terms of the progressive decline of the parasite rate, total absence of fresh infections, and immediate reduction to zero of the parasite rate among infants born after the start of the campaign. However, since it is statistically impossible to prove absolute success which is tolerable for the purposes of eradication, and statistically sound criteria should be set up to enable the
Assuntos
Malária/transmissão , Malária/epidemiologia , Plasmodium falciparum , Monitoramento EpidemiológicoRESUMO
Present methods for assessment of the attack phase of malaria eradication are inadequate, particularly lacking any objective parasitological criteria of success. The most objective of the criteria used has been the absence of infections among infants. This has always been subject to the drawback that it is rarely possible to get enough infants to secure a statistically reliable result. Moreover, all the variants used have been subject to the difficulty that it is impossible to prove a total negative without examination of the entire population, and there has always been uncertainty on the scale of examination which was required for adequacy. The authors have therefore undertaken a careful review of parasitological criteria for the interruption of transmission, with the intention of producing precise and objective criteria from which clear-cut conclusions could be reached on the adequacy of the attack mechanism. In theory the total interruption of transmission should produce readily foreseeable results in terms of the progressive decline of the parasite rate, total absence of fresh infections, and immediate reduction to zero of the parasite rate among infants born after the start of the campaign. However, since it is statistically impossible to prove absolute success which is tolerable for the purposes of eradication, and statistically sound criteria should be set up to enable the
