STUDIES ON THE CHARACTERIZATION AND STRUCTURE OF THE IMMOBILIZATION ANTIGENS OF PARAMECIUM AURELIA.
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ABSTRACT:
SUBMITTER: JONES IG
PROVIDER: S-EPMC1206902 | biostudies-other | 1965 Jul
REPOSITORIES: biostudies-other
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Project description:We have developed a procedure to isolate the ciliary membranes of Paramecium and have analysed the membrane proteins by electrophoresis on polyacrylamide gels containing either Triton X-100 or sodium dodecyl sulphate. The electrophoretic pattern on gels containing sodium dodecyl sulphate showed 12-15 minor bands of mol.wt. 25 000-150 000 and on major band of mol.wt. 200 000-300 000 that contained approximately three-quarters of the total membrane protein. 2. We present evidence that the major membrane protein is related to, but not identical with, the immobilization antigen (i-antigen), which is a large (250 000 mol.w.), soluble, surface protein of Paramecium. The similarity of the i-antigen and the major membrane protein was shown by immunodiffusion and by the electrophoretic mobilities in sodium dodecyl sulphate of these two proteins from Paramecium of serotypes A and B. The non-identity of these two proteins was shown by their different electrophoretic mobilities on Triton X-100 containing gels and their different solubilities. 3. We propose that the major membrane protein and the i-antigen have a precursor-product relationship.
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Project description:UNLABELLED:Antigenic or phenotypic variation is a widespread phenomenon of expression of variable surface protein coats on eukaryotic microbes. To clarify the mechanism behind mutually exclusive gene expression, we characterized the genetic properties of the surface antigen multigene family in the ciliate Paramecium tetraurelia and the epigenetic factors controlling expression and silencing. Genome analysis indicated that the multigene family consists of intrachromosomal and subtelomeric genes; both classes apparently derive from different gene duplication events: whole-genome and intrachromosomal duplication. Expression analysis provides evidence for telomere position effects, because only subtelomeric genes follow mutually exclusive transcription. Microarray analysis of cultures deficient in Rdr3, an RNA-dependent RNA polymerase, in comparison to serotype-pure wild-type cultures, shows cotranscription of a subset of subtelomeric genes, indicating that the telomere position effect is due to a selective occurrence of Rdr3-mediated silencing in subtelomeric regions. We present a model of surface antigen evolution by intrachromosomal gene duplication involving the maintenance of positive selection of structurally relevant regions. Further analysis of chromosome heterogeneity shows that alternative telomere addition regions clearly affect transcription of closely related genes. Consequently, chromosome fragmentation appears to be of crucial importance for surface antigen expression and evolution. Our data suggest that RNAi-mediated control of this genetic network by trans-acting RNAs allows rapid epigenetic adaptation by phenotypic variation in combination with long-term genetic adaptation by Darwinian evolution of antigen genes. IMPORTANCE:Alternating surface protein structures have been described for almost all eukaryotic microbes, and a broad variety of functions have been described, such as virulence factors, adhesion molecules, and molecular camouflage. Mechanisms controlling gene expression of variable surface proteins therefore represent a powerful tool for rapid phenotypic variation across kingdoms in pathogenic as well as free-living eukaryotic microbes. However, the epigenetic mechanisms controlling synchronous expression and silencing of individual genes are hardly understood. Using the ciliate Paramecium tetraurelia as a (epi)genetic model, we showed that a subtelomeric gene position effect is associated with the selective occurrence of RNAi-mediated silencing of silent surface protein genes, suggesting small interfering RNA (siRNA)-mediated epigenetic cross talks between silent and active surface antigen genes. Our integrated genomic and molecular approach discloses the correlation between gene position effects and siRNA-mediated trans-silencing, thus providing two new parameters for regulation of mutually exclusive gene expression and the genomic organization of variant gene families.
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