RESUMO
In an analysis of 22 of the roughly 100 dispersed 5S rRNA genes in Neurospora crassa, a methylated 5S rRNA pseudogene, Psi63, was identified. We characterized the Psi63 region to better understand the control and function of DNA methylation. The 120-bp 5S rRNA-like region of Psi63 is interrupted by a 1.9-kb insertion that has characteristics of sequences that have been modified by repeat-induced point mutation (RIP). We found sequences related to this insertion in wild-type strains of N. crassa and other Neurospora species. Most showed evidence of RIP; but one, isolated from the N. crassa host of Psi63, showed no evidence of RIP. A deletion from near the center of this sequence apparently rendered it incapable of participating in RIP with the related full-length copies. The Psi63 insertion and the related sequences have features of transposons and are related to the Fot1 class of fungal transposable elements. Apparently Psi63 was generated by insertion of a previously unrecognized Neurospora transposable element into a 5S rRNA gene, followed by RIP. We name the resulting inactivated Neurospora transposon PuntRIP1 and the related sequence showing no evidence of RIP, but harboring a deletion that presumably rendered it defective for transposition, dPunt.
Assuntos
Elementos de DNA Transponíveis , Genes Fúngicos , Neurospora crassa/genética , Pseudogenes , RNA Fúngico/genética , RNA Ribossômico 5S/genética , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Primers do DNA/genética , DNA Fúngico/genética , Metilação , Dados de Sequência Molecular , Neurospora crassa/química , Mutação Puntual , RNA Fúngico/química , RNA Ribossômico 5S/química , Sequências Repetitivas de Ácido Nucleico , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido NucleicoRESUMO
Cytosine methylation has been implicated in epigenetic control of gene expression in animals, plants, and fungi. It has been assumed that all methylation in eukaryotes is at symmetrical sequences such as CpG/GpC, because this can explain perpetuation of methylation states. Here the bisulfite genomic sequencing method was used to examine methylation in DNA from a Neurospora gene exposed to repeat-induced point mutation. 5-Methylcytosine was not limited to symmetrical sites and individual molecules showed different patterns and amounts of modification. The methylation extended beyond the mutated region and even beyond the edge of the duplicated segment.
