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Comment
. 2007 May 29;104(22):9107-8.
doi: 10.1073/pnas.0703224104. Epub 2007 May 21.

The beginning of the end: links between ancient retroelements and modern telomerases

M Joan Curcio  1 , Marlene Belfort
Affiliations
Comment

The beginning of the end: links between ancient retroelements and modern telomerases

M Joan Curcio et al. Proc Natl Acad Sci U S A. .
No abstract available

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Telomerases and retrotransposons. (A) RTs at telomere and within chromosome (black lines with gray circle). TERT acts on 3′-OH at telomere, whereas the RT of endonuclease-proficient TP-retrotransposons acts on the 3′-OH at a double-strand break. The wavy line indicates RNA. (B) Structure. The canonical nuclease-proficient PLE consists of a single ORF comprising RT and a GIY-YIG endonuclease. Terminal PLEs lack the endonuclease domain, but contain a 5′ ORF with similarity to ORF1 of L1 elements, depicted below. The RT of L1 contains an AP-endonuclease domain (AP, apurinic/apyrimidinic). (C) Mechanism. PLE retrotransposition occurs when repeat sequences near the 3′ end of PLE RNA hybridize to a telomeric DNA repeat (TGAGGG) at the single-stranded 3′ end of the chromosome. With the 3′ OH as a primer, RT synthesizes cDNA (blue) from the PLE RNA template. The second (bottom) strand of DNA is presumably synthesized by host-mediated DNA replication. RT dissociates from the PLE RNA prematurely, creating a 5′ truncated cDNA, which is capped with telomeric DNA repeats (purple) by telomerase. Retrotransposition of the endonuclease-deficient L1 element begins when the 3′ poly(A) tail of L1 RNA associates with the 3′ end of a dysfunctional telomere. RT synthesizes cDNA by using the L1 RNA temple. (D) Evolution. The schematic shows the ancestral RT giving rise to telomerase or a retrotransposon, which can revert to the primordial-RT-like state.
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