A novel reverse transcriptase activity associated with mitochondrial plasmids of Neurospora

Area of Science:

• Mitochondrial genetics
• Molecular biology
• Retrotransposon research

Background:

• Mauriceville and Varkud mitochondrial plasmids in Neurospora are related DNA elements.
• Their genetic organization suggests links to retrotransposons and mitochondrial introns.
• Both plasmids potentially encode a reverse transcriptase-like protein.

Purpose of the Study:

• To investigate the reverse transcriptase activity in Neurospora mitochondrial plasmids.
• To elucidate the mechanism of DNA synthesis by these plasmids.
• To explore the evolutionary relationship between plasmid reverse transcription and retroviral mechanisms.

Main Methods:

• Analysis of mitochondrial RNP preparations from Mauriceville and Varkud strains.
• Assaying for reverse transcriptase activity specific to endogenous plasmid RNA.
• Characterization of the synthesized DNA and its relationship to plasmid transcripts.

Main Results:

• Mitochondria from Mauriceville and Varkud strains exhibit specific reverse transcriptase activity.
• The enzyme synthesizes full-length minus-strand DNA from plasmid RNA.
• Synthesis initiates at the 3' end of the transcript, which has tRNA-like features.

Conclusions:

• Neurospora mitochondrial plasmids utilize a novel reverse transcription mechanism.
• This mechanism may involve tRNA-like structures at the 3' end of self-replicating RNAs.
• The observed mechanism could be an ancestral form of the standard retroviral mechanism.