Nucleic Acids Research, 2000, Vol. 28, No. 7 1514-1524
© 2000 Oxford University Press
Characterization of an unusual tRNA-like sequence found inserted in a Neurospora retroplasmid
The publisher would like to apologise for an error in the above paper: tmRNA was incorrectly published as mtRNA throughout the paper. The corrected paper is printed in full on the following pages.
1Institute for Cellular and Molecular Biology, Department of Chemistry and Biochemistry and Section of Molecular Genetics and Microbiology, School of Biological Sciences, University of Texas at Austin, Austin, TX 78712, USA, 2Departments of Molecular Genetics and Biochemistry, The Ohio State University, Columbus, OH 43210, USA and 3Department of Microbiology, Michigan State University, East Lansing, MI 48824, USA
ABSTRACT
We characterized an unusual tRNA-like sequence that had been found inserted in suppressive variants of the mitochondrial retroplasmid of Neurospora intermedia strain Varkud. We previously identified two forms of the tRNA-like sequence, one of 64 nt (TRL-64) and the other of 78 nt (TRL-78) containing a 14-nt internal insertion in the anticodon stem at a position expected for a nuclear tRNA intron. Here, we show that TRL-78 is encoded in Varkud mitochondrial (mt)DNA within a 7 kb sequence that is not present in Neurospora crassa wild-type 74A mtDNA. This 7-kb insertion also contains a perfectly duplicated tRNATrp gene, segments of several mitochondrial plasmids and numerous GC-rich palindromic sequences that are repeated elsewhere in the mtDNA. The mtDNA-encoded copy of TRL-78 is transcribed and apparently undergoes 5'- and 3'-end processing and 3' nucleotide addition by tRNA nucleotidyl transferase to yield a discrete tRNA-sized molecule. However, the 14 nt intron-like sequence in TRL-78, which is missing in the TRL-64 form, is not spliced detectably in vivo or in vitro. Our results show that TRL-78 is an unusual tRNA-like species that could be incorporated into suppressive retroplasmids by the same reverse transcription mechanism used to incorporate mt tRNAs. The tRNA-like sequence may have been derived from an intron-containing nuclear tRNA gene or it may serve some function, like tmRNA. Our results suggest that mt tRNAs or tRNA-like species may be integrated into mtDNA via reverse transcription, analogous to SINE elements in animal cells.
FOOTNOTES
* To whom correspondence should be addressed at: Institute for Cellular and Molecular Biology, Department of Chemistry and Biochemistry and Section of Molecular Genetics and Microbiology, School of Biological Sciences, University of Texas at Austin, Austin, TX 78712, USA. Tel: +1 512 232 3418; Fax: +1 512 232 3420; Email: lambowitz@mail.utexas.edu Present address: Leslie A. Wanner, The Norwegian Crop Research Institute, Plant Pathology Department, Høgskoleveien 7, N-1432 Aas, Norway