Gag Proteins of the Two Drosophila Telomeric Retrotransposons Are Targeted to Chromosome Ends

• Published in: The Journal of cell biology 2002-11, Vol.159 (3), p.397-402
• Main Authors: Rashkova, Svetlana, Karam, Sarah E., Kellum, Rebecca, Pardue, Mary-Lou
• Format: Article
• Language: English
• Subjects: Animals; Cell nucleus; Cell Nucleus - metabolism; Cells; Cells, Cultured; Cellular biology; Chromosomes; DNA Transposable Elements; Drosophila; Drosophila melanogaster - genetics; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Gene Products, gag; Genes; Genetic transposition; Green Fluorescent Proteins; Indicators and Reagents - metabolism; Insect Proteins - genetics; Insect Proteins - metabolism; Insects; Interphase; Luminescent Proteins - genetics; Luminescent Proteins - metabolism; Microscopy, Fluorescence; Proteins; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Retroelements - genetics; Retrotransposons; Tarts; Telomere - genetics; Telomere - metabolism; Telomeres; Transposons
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200205039

Drosophila telomeres are formed by two non-LTR retrotransposons, HeT-A and TART, which transpose only to chromosome ends. Successive transpositions of these telomeric elements yield arrays that are functionally equivalent to the arrays generated by telomerase in other organisms. In contrast, other Drosophila non-LTR retrotransposons transpose widely through gene-rich regions, but not to ends. The two telomeric elements encode very similar Gag proteins, suggesting that Gag may be involved in their unique targeting to chromosome ends. To test the intrinsic potential of these Gag proteins for targeting, we tagged the coding sequences with sequence of GFP and expressed the constructs in transiently transfected Drosophila-cultured cells. Gag proteins from both elements are efficiently transported into the nucleus where the protein from one element, HeT-A, forms structures associated with chromosome ends in interphase nuclei. Gag from the second element, TART, moves into telomere-associated structures only when co-expressed with HeT-A Gag. The results suggest that these Gag proteins are capable of delivering the retrotransposons to telomeres, although TART requires assistance from HeT-A. They also imply a symbiotic relationship between the two elements, with HeT-A Gag directing the telomere-specific targeting of the elements, whereas TART provides reverse transcriptase for transposition.