Target-Primed Mobilization Mechanisms

Abstract

Synonyms Target-primed reverse transcription Synopsis Some genetic elements utilize a free 3 0 OH at a new genetic location to prime DNA synthesis, resulting in a copy of the element in the target DNA. In a simple example of this mechanism, homing endonucleases are encoded within mobile elements, which are used to create a double-strand DNA break(s) in a target DNA molecule. By creating a double-strand DNA break(s), the host genome is activated for homologous recombination, and the mobile element is copied into that DNA site; the 3 0 ends from one of the broken DNA are used to prime synthesis of the element. Other mobile elements use a process termed target-primed reverse transcription to move via an RNA intermediate. Following transcription of the DNA element, the RNA copy is reverse transcribed into a new DNA site, using a nick in the DNA at that site to prime reverse transcription. There are two major classes of elements that move by a target-primed reverse transcription mechanism, the non-LTR retrotransposons and the group II mobile introns. Non-LTR (non-long terminal repeat) retrotransposons are copied out of their original location by a host-encoded RNA polymerase and directly copied back into a new location by an element-encoded reverse transcriptase. Group II mobile introns excise themselves from a larger mRNA molecule and use a reverse transcriptase to make a DNA copy at a new site. This process also involves the priming of DNA synthesis by a free 3 0 OH at the target site.