The Y chromosome of Drosophila melanogaster contains a distinctive subclass of Het-A-related repeats.
The HeT-A element is a transposable element with an apparent role in the structure of the telomeres of Drosophila melanogaster chromosomes. HeT-A transposition is the earliest event detected in healing of broken ends; HeT-A is also found on telomeres of unbroken chromosomes. Sequences with homology to HeT-A are never detected in euchromatic regions; however, clusters of HeT-A-related sequences occur in nontelomeric regions of the heterochromatic Y chromosome. Analysis of two of these Y-associated clusters shows them to be significantly different in structure from telomeric HeT-A elements, although the regions of shared sequence have > 80% sequence identity in all cases. Telomeric HeT-A elements occur in chains, with the elements in the same orientation but variably truncated at their external ends and irregularly interspersed with unrelated sequences. In contrast, the nontelomeric Y elements are regular tandem repeats of parts of the HeT-A sequence joined to unrelated sequences which are not the same in the two clusters studied. The sequence structures suggest that the nontelomeric clusters on the Y chromosome do not arise by the same transposition mechanism that forms the telomeric clusters; instead the clusters on the Y may arise by a mechanism that is used more generally in the evolution of Y chromosomes. Although the telomeric and nontelomeric clusters appear to be formed differently, both are enriched in parts of the HeT-A sequence which may be important in the structure of heterochromatin.
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
O
O
Danilevskaya
A
A
Lofsky
E V
EV
Kurenova
M L
ML
Pardue
D000818:Animals; D016384:Consensus Sequence; D004251:DNA Transposable Elements / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D008297:Male; D012091:Repetitive Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D016615:Telomere; D014998:Y Chromosome
D004251:DNA Transposable Elements