The VS catalytic RNA replicates by reverse transcription as a satellite of a retroplasmid.
The mitochondria of certain natural isolates of Neurospora contain both the Varkud plasmid, which encodes a reverse transcriptase, and a small unrelated RNA (VS RNA) that performs RNA-mediated self-cleavage and ligation reactions. Here, we show that VS RNA is transcribed from a VS plasmid DNA template by the Neurospora mitochondrial RNA polymerase using a promoter located immediately upstream of the RNA self-cleavage site that generates monomeric transcripts. VS RNA is then reverse transcribed by the Varkud plasmid reverse transcriptase to yield a full-length (-) strand cDNA, a predicted replication intermediate. Combined with previous genetic evidence, our results indicate that the VS plasmid replicates by reverse transcription as a satellite of the Varkud plasmid. This mode of replication, unprecedented for a satellite RNA, likely reflects the promiscuity of the Varkud plasmid reverse transcriptase, which does not require a specific primer to initiate cDNA synthesis. Our findings indicate how primitive reverse transcriptases with similar relaxed specificity could have facilitated the evolution of new retroelements.
Kennell
J C
JC
Department of Molecular Genetics, Ohio State University, Columbus 43210-1292.
Saville
B J
BJ
Mohr
S
S
Kuiper
M T
MT
Sabourin
J R
JR
Collins
R A
RA
Lambowitz
A M
AM
D001483:Base Sequence; D015152:Blotting, Northern; D018076:DNA, Complementary; D004272:DNA, Mitochondrial / Q000235:genetics*; D008969:Molecular Sequence Data; D009491:Neurospora / Q000201:enzymology / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D012313:RNA / Q000235:genetics*; D019244:RNA, Satellite; D012194:RNA-Directed DNA Polymerase / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics; D014721:Vesicular stomatitis Indiana virus / Q000235:genetics*
D018076:DNA, Complementary; D004272:DNA, Mitochondrial; D019244:RNA, Satellite; D012313:RNA; D012194:RNA-Directed DNA Polymerase