TRANSPOSONS IN-PLACE OF TELOMERIC REPEATS AT A DROSOPHILA TELOMERE

We present the first isolation of the terminal DNA of an intact Drosop hila telomere. lt differs from those isolated from other eukaryotes by the lack of short tandem repeats at the terminus. The terminal 14.5 k b is composed of four tandem elements derived from two families of non -long terminal repeat retrotransposons and is subject to slow terminal loss. One of these transposon families, TART (telomere-associated ret rotransposon), is described for the first time here. The other element , HeT-A, has previously been shown to transpose to broken chromosome e nds. Our results provide key evidence that these elements also transpo se to natural chromosome ends. We propose that the telomere-associated repetitive DNA is maintained by saltatory expansions, including termi nal transpositions of specialized retrotransposons, which serve to bal ance terminal loss.