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Foret1, a reverse transcriptase-like sequence in the filamentous fungus Fusarium oxysporum.

ABSTRACT: We report here the isolation of Foret1, a repeated DNA sequence cloned from the fungal plant pathogen Fusarium oxysporum. This clone exhibits a high degree of sequence similarity with the retroviral pol genes. Sequences homologous to protease, reverse transcriptase, ribonuclease H are found in that order. The overall structure is homologous to the 'gypsy' class of LTR-retrotransposons. Its similarity to elements present in widely different organisms may result from its horizontal transmission in recent evolutionary time.

SUBMITTER: Julien J

PROVIDER: S-EPMC334069 | biostudies-other | 1992 Aug

REPOSITORIES: biostudies-other

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Foret1, a reverse transcriptase-like sequence in the filamentous fungus Fusarium oxysporum.

Julien J J Poirier-Hamon S S Brygoo Y Y

Nucleic acids research 19920801 15

We report here the isolation of Foret1, a repeated DNA sequence cloned from the fungal plant pathogen Fusarium oxysporum. This clone exhibits a high degree of sequence similarity with the retroviral pol genes. Sequences homologous to protease, reverse transcriptase, ribonuclease H are found in that order. The overall structure is homologous to the 'gypsy' class of LTR-retrotransposons. Its similarity to elements present in widely different organisms may result from its horizontal transmission in ...[more]

PMID: 1380691

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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

Foret1, a reverse transcriptase-like sequence in the filamentous fungus Fusarium oxysporum.

Publications

Foret1, a reverse transcriptase-like sequence in the filamentous fungus Fusarium oxysporum.

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