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Another example of a eukaryotic transposable element is the TY element of yeast. This element has several features that are unique, and it appears to resemble a primitive retrovirus. A retrovirus is a RNA virus that, after being uncoated in the host cell, converts its RNA to a DNA copy by the enzyme reverse transcriptase. This enzyme is encoded by the retroviral pol gene. The DNA copy of the retrovirus is inserted into the eukaryotic genome, and it remains there as a provirus until it is excised and undergoes transcription to produce new viral particles.
Features of TY elements
- about 35 copies in the haploid yeast gene
- has an about 340 bp sequence at both ends in a direct orientation; these are called long terminal repeats or LTRs
- resemble eukaryotic retroviruses; because they lack some of the retroviral functions they are considered to be primitive retroviruses; because of their similarities they are called retrotransposons
- transposition involves an RNA intermediate that is generated by transcription of the TY element; a reverse transcriptase (encoded by the TyB gene of the element) makes a DNA copy of the element which is then inserted into a new site in the yeast genome
Copyright ? 1997. Phillip McClean
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