THE ENIGMA OF Y-CHROMOSOME DEGENERATION - TRAM, A NOVEL RETROTRANSPOSON IS PREFERENTIALLY LOCATED ON THE NEO-Y CHROMOSOME OF DROSOPHILA-MIRANDA

We have cloned a novel transposable element from the neo-Y chromosome of Drosophila miranda. The size of the element, designated as TRAM, is 3.452 bp, including on both sides long terminal direct repeats (LTRs) of 372 bp, respectively. The element is flanked by a 5-bp target site duplication; ATATG. The putative primer binding site (PBS) for minus- strand priming is complementary to 18 nucleotides of the 3'-end of tRN A(Trp). Data base screens for DNA sequence identities were negative, a part from the sequence motif of the PBS. The deduced amino acid sequen ce from the large ORF does got reveal identities described for other t ransposons. In situ hybridizations with TRAM subclones show a biased d istribution in the genome, with a massive accumulation of TRAM in the neo-Y chromosome, while the former homologue, the X2 chromosome is dev oid of TRAM sites. The enriched occurrence of the TRAM element at the evolving neo-Y chromosome of D.miranda adds compelling evidence in fav or of the view that Y chromosome degeneration is driven by the accumul ation of transposable elements.