Reverse transcriptase can stabilize or destabilize the genome

Telomeres, the eukaryotic chromosome termini, are deoxyribonucleoprotein st ructures that distinguish natural chromosome ends from broken DNA. In most organisms, telomeres are extended by a reverse transcriptase (RT) with an i ntegrated RNA template, telomerase; in Drosophila melanogaster, however, te lomere-specific retrotransposons, HeT-A and TART, transpose specifically to chromosome ends. Whether telomeres are extended by a telomerase or by retr otransposons, an RT is a key component. RT has been studied extensively, bo th for its important role in converting RNA genomes to DNA, which has great evolutionary impact, and as a therapeutic target in human retroviral disea ses. Here we discuss a few important aspects of RT usage during retrotransp osition and telomere elongation.