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Linear mitochondrial plasmids of Fusarium oxysporum contain genes with sequence similarity to genes encoding a reverse transcriptase from Neurospora spp.

ABSTRACT: Two linear mitochondrial plasmids called pFOXC1 and pFOXC2 from the fungus Fusarium oxysporum were previously described. DNA sequence comparisons indicated that the derived amino acid sequences of both plasmids exhibit similarity to the reverse transcriptase of the Mauriceville and Varkud plasmids of Neurospora spp. The derived amino acid sequence of pFOXC2 has 51% similarity and 32% identity to the Neurospora reverse transcriptase; sequence similarity was greatest for seven blocks of amino acids that are conserved in reverse transcriptases from a wide range of biological sources. Northern analysis suggests that full-length RNAs corresponding to the plasmids are found in representative isolates.

SUBMITTER: Kistler HC

PROVIDER: S-EPMC168633 | biostudies-other | 1997 Aug

REPOSITORIES: biostudies-other

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Linear mitochondrial plasmids of Fusarium oxysporum contain genes with sequence similarity to genes encoding a reverse transcriptase from Neurospora spp.

Kistler H C HC Benny U U Powell W A WA

Applied and environmental microbiology 19970801 8

Two linear mitochondrial plasmids called pFOXC1 and pFOXC2 from the fungus Fusarium oxysporum were previously described. DNA sequence comparisons indicated that the derived amino acid sequences of both plasmids exhibit similarity to the reverse transcriptase of the Mauriceville and Varkud plasmids of Neurospora spp. The derived amino acid sequence of pFOXC2 has 51% similarity and 32% identity to the Neurospora reverse transcriptase; sequence similarity was greatest for seven blocks of amino acid ...[more]

PMID: 9251222

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Project description:BACKGROUND:The pFOXC retroplasmids are small, autonomously replicating DNA molecules found in mitochondria of certain strains of the filamentous fungus Fusarium oxysporum and are among the first linear genetic elements shown to replicate via reverse transcription. The plasmids have a unique clothespin structure that includes a 5'-linked protein and telomere-like terminal repeats, with pFOXC2 and pFOXC3 having iterative copies of a 5 bp sequence. The plasmids contain a single large open reading frame (ORF) encoding an active reverse transcriptase (RT). The pFOXC-RT is associated with the plasmid transcript in a ribonucleoprotein (RNP) complex and can synthesize full-length (-) strand cDNA products. In reactions containing partially purified RT preparations with exogenous RNAs, the pFOXC3-RT has been shown to initiate cDNA synthesis by use of snapped-back RNAs, as well as loosely associated DNA primers. RESULTS:The complete sequence of the distantly related pFOXC1 plasmid was determined and found to terminate in 3-5 copies of a 3 bp sequence. Unexpectedly, the majority of (-) strand cDNA molecules produced from endogenous pFOXC1 transcripts were attached to protein. In vitro experiments using partially purified pFOXC3-RT preparations having a single radiolabeled deoxyribonucleotide triphosphate (dNTP) generated a nucleotide-labeled protein that migrated at the size of the pFOXC-RT. The nucleotide preference of deoxynucleotidylation differed between pFOXC3 and pFOXC1 and showed complementarity to the respective 3' terminal repeats. In reactions that include exogenous RNA templates corresponding to the 3' end of pFOXC1, a protein-linked cDNA product was generated following deoxynucleotidylation, suggesting that reverse transcription initiates with a protein primer. CONCLUSIONS:The finding that reverse transcription is protein primed suggests the pFOXC retroplasmids may have an evolutionary relationship with hepadnaviruses, the only other retroelement family known to initiate reverse transcription via a protein primer. Moreover, the similarity to protein-primed linear DNA elements supports models in which the terminal repeats are generated and maintained by a DNA slideback mechanism. The ability of the pFOXC-RT to utilize RNA, DNA and protein primers is unique among polymerases and suggests that the pFOXC plasmids may be evolutionary precursors of a broad range of retroelements, including hepadnaviruses, non-long terminal repeat (non-LTR) retrotransposons and telomerase.

Dataset Information

Linear mitochondrial plasmids of Fusarium oxysporum contain genes with sequence similarity to genes encoding a reverse transcriptase from Neurospora spp.

Publications

Linear mitochondrial plasmids of Fusarium oxysporum contain genes with sequence similarity to genes encoding a reverse transcriptase from Neurospora spp.

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