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pCal, a highly unusual Ty1/copia retrotransposon from the pathogenic yeast Candida albicans
G D Matthews1, T J Goodwin, M I Butler
1Department of Biochemistry, University of Otago, Dunedin, New Zealand.
Abstract:
Retrotransposons are mobile genetic elements. They can transpose via the reverse transcription of mRNA into double-stranded DNA (dsDNA) followed by the insertion of this dsDNA into new sites within the host genome. The unintegrated, linear, dsDNA form of retrotransposons is usually very rare. We report here the isolation of a retrotransposon from Candida albicans which is unusual in this respect. This element, which we have named pCal, was first identified as a distinct band when uncut C. albicans DNA was examined on an agarose gel. Sequence analysis of the cloned element revealed that it is a retrotransposon belonging to the Ty1/copia group. It is estimated that pCal produces 50 to 100 free, linear, dsDNA copies of itself per cell. This is a much higher level of expression than even that of the system in which Ty1 is expressed behind the highly active GAL1 promoter on a high-copy-number plasmid (about 10 copies per cell). Another unusual feature of pCal is that its Pol enzymes are likely to be expressed via the pseudoknot-assisted suppression of an upstream, in-phase stop codon, as has been shown for Moloney murine leukemia virus.
Insights
Researchers discovered a novel retrotransposon, pCal, in Candida albicans. This mobile genetic element unusually produces high levels of free DNA copies, offering new insights into retrotransposon biology.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Retrotransposons are mobile genetic elements that replicate via reverse transcription of mRNA into double-stranded DNA (dsDNA).
- The unintegrated, linear dsDNA form of retrotransposons is typically rare in host genomes.
- Candida albicans is a significant human fungal pathogen with a complex genome.
Purpose of the Study:
- To isolate and characterize a novel retrotransposon from Candida albicans.
- To investigate the unusual abundance of free, linear dsDNA copies of this element.
- To elucidate the expression mechanism of the pCal retrotransposon's Pol enzymes.
Main Methods:
- Agarose gel electrophoresis to identify distinct DNA bands in uncut C. albicans DNA.
- Sequence analysis of the isolated retrotransposon element.
- Estimation of free, linear dsDNA copy number per cell.
- Comparative analysis of expression levels with known retrotransposon systems.
Main Results:
- Isolation and identification of a novel Ty1/copia group retrotransposon, named pCal, from Candida albicans.
- pCal produces an exceptionally high level of free, linear dsDNA copies (50-100 per cell), significantly exceeding previously reported levels.
- Pol enzyme expression in pCal is likely mediated by pseudoknot-assisted ribosomal frameshifting, similar to Moloney murine leukemia virus.
Conclusions:
- pCal represents a unique retrotransposon with an unusually high rate of free dsDNA production.
- The high copy number suggests a potentially significant role for pCal in the C. albicans genome.
- The identified mechanism for Pol enzyme expression provides new insights into retrotransposon regulation.