Jc. Kennell et al., THE VS CATALYTIC RNA REPLICATES BY REVERSE TRANSCRIPTION AS A SATELLITE OF A RETROPLASMID, Genes & development, 9(3), 1995, pp. 294-303
The mitochondria of certain natural isolates of Neurospora contain bot
h the Varkud plasmid, which encodes a reverse transcriptase, and a sma
ll unrelated RNA (VS RNA) that performs RNA-mediated self-cleavage and
ligation reactions. Here, we show that VS RNA is transcribed from a V
S 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 tra
nscribed by the Varkud plasmid reverse transcriptase to yield a full-l
ength (-) strand cDNA, a predicted replication intermediate. Combined
with previous genetic evidence, our results indicate that the VS plasm
id replicates by reverse transcription as a satellite of the Varkud pl
asmid. This mode of replication, unprecedented for a satellite RNA, li
kely reflects the promiscuity of the Varkud plasmid reverse transcript
ase, which does not require a specific primer to initiate cDNA synthes
is. Our findings indicate how primitive reverse transcriptases with si
milar relaxed specificity could have facilitated the evolution of new
retroelements.