| Abstrakt: |
Microdissection and microcloning of the Y chromosomal lampbrush loop pseudonucleolus from primary spermatocytes of Drosophila hydei allowed the isolation of copies of a 0.2 kb tandemly repeated DNA sequence family (dhMiP14.1). In situ hybridization confirmed its origin from a distal position in the long arm of the Y chromosome. Transcript in situ hybridization showed that at least some of the repeat units are part of the transcripts of lampbrush loops. The characterization of this DNA sequence revealed cross-homology to the ß2 region of the 26 S rRNA gene, 600 bp downstream of the intervening sequence (IVS) insertion site. The cloned DNA sequence, however, cannot be part of the rDNA repeats since it occurs as a 0.2 kb tandem repeat in the Y chromosome. We therefore named the DNA sequence the “rally” (ribosomal and lampbrush loop Y chromosome) sequence. The different repeat units of the 0.2 kb sequence display a moderate degree of divergence. They are not found in the closely related species D. neohydei or D. eohydei, nor in D. melanogaster. We assume that this Y chromosomal DNA sequence is the result of a recent transposition into the Y chromosomal location, followed by an amplification event. It is an important observation that the 0.2 kb sequence also occurs in the neighbouring lampbrush loop “threads”. Since other DNA sequences are also found in both loops, the assumption of a functional relationship between both loop pairs, derived from genetic observations, is further supported. |
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