Retro Elements Make an RNA Copy

The transposons we have discussed so far move while in their DNA form. In addition, there is a vast array of mobile elements that move while in their RNA phase. These range from retroviruses (see Ch. 17), which can integrate their DNA into the host cell chromosome, to transposon-like elements. These may all be classed as retro-elements since they all use reverse transcriptase to convert an RNA transcript back into DNA. Whenever retro-elements insert into host DNA the target sequence is duplicated as for DNA-based transposons. Retro-elements are more common in higher organisms whereas DNA-based transposons predominate in bacteria.

Retrotransposons or (for short) retroposons are transposable elements that rely on reverse transcriptase for movement.They are found most often in eukaryotes, especially animals. The Ty1 (Transposon of yeast 1) retrotransposon of yeast is around 6,000 bp

Mariner elements A widespread family of conservative DNA-based transposons first found in Drosophila retro-element A genetic element that uses reverse transcriptase to convert the RNA form of its genome to a DNA copy retroposon Short for retrotransposon retrotransposon A transposable element that uses reverse transcriptase to convert the RNA form of its genome to a DNA copy reverse transcriptase Enzyme that synthesizes a DNA copy from an RNA template

Ty1 element Transposon yeast 1. A retrotransposon of yeast that moves via an RNA intermediate

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TyA and TyB overlap by 13 codons

FIGURE 15.16 Structure of Ty-1 Retrotransposon

Ty-1 is flanked by two direct repeats (LTRs) and contains the genes for reverse transcriptase and a DNA binding regulatory protein. Reverse transcriptase is only produced if a frameshift occurs during translation. If no frameshift occurs, the truncated gene product binds to DNA and acts as a regulatory protein.

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