Developmentally Regulated Ribosomal rDNA Genes in Plasmodium vivax: Biological Implications and Practical Applications
Uniformed Services University Of The Health Sciences Bethesda United States
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Ribosomal RNA rRNA is an essential determinant of the structure and function of the ribosome, a ubiquitous apparatus for protein synthesis. In contrast to othereukaryotes, the rRNA genes in Plasmodium species are unique in terms of their genomic arrangement and transcriptional regulation during development further investigation may elucidate the functional significance of the gene organization to parasite development and evolution. In this study, three structurally distinct rRNA genes, including one novel type, have been characterized from the genomic DNA of the human malaria parasite, Plasmodium vivax. Comparison of the sequences coding for small subunit rRNA SSUrRNA indicates that the type A gene seems to be closely related to the type C gene with an overall similarity of 85.5 while the type B gene, the novel type, appears more distantly related to either the A or C gene. It has an overall similarity to the A and C genes of 52 and 62, respectively. The sequence differences are not randomly distributed but tend to cluster into several regions known to diverge rapidly in all eukaryotic SSUrRNAs. Comparative analysis of the secondary structures suggests that all three transcripts retain the essential conformation conserved in eukaryotic rRNAs. The structural differences occurring between the genes are localized to three predicted variable regions and appear to be characteristic of the gene type rather than the species of origin. This is also true in the corresponding genes from closely related species of the genus Plasmodium. The existence of these structurally distinct rRNAs within all Plasmodium species studied may indicate a functional significance to maintaining the multi-rRNA system. Transcription of the three distinct genes is differentially regulated during the discrete stages of P. vivax development. The A gene transcript is predominant during erythrocytic schizogony in the human host and disappears after 24 hours in engorged mosquitoes.