A Methylated Neurospora 5S rRNA Pseudogene Contains a Transposable Element Inactivated by Repeat-Induced Point Mutation

Corresponding author: Eric U. Selker, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403., selker{at}molbio.uoregon.edu (E-mail).

Communicating editor: R. H. DAVIS

In an analysis of 22 of the roughly 100 dispersed 5S rRNA genes in Neurospora crassa, a methylated 5S rRNA pseudogene, ₆₃, was identified. We characterized the ₆₃ region to better understand the control and function of DNA methylation. The 120-bp 5S rRNA-like region of ₆₃ 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 ₆₃, 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 ₆₃ insertion and the related sequences have features of transposons and are related to the Fot1 class of fungal transposable elements. Apparently ₆₃ 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 Punt^RIP1 and the related sequence showing no evidence of RIP, but harboring a deletion that presumably rendered it defective for transposition, dPunt.

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