A spontaneously opened ring chromosome of Drosophila melanogaster has acquired He-T DNA sequences at both new telomeres.

Ring chromosomes that have been opened to give linear chromosomes offer an opportunity to study the DNA sequences associated with new chromosome ends. The Drosophila melanogaster chromosome C(1)A was originally a ring chromosome, consisting of two linked X chromosomes, and thus had no telomeres. This chromosome has spontaneously opened in polytene region 13, a region near the middle of the euchromatic arm of the X chromosome. The opening of the ring has produced two new telomeres on the C(1)A chromosome. Each of the new telomeres has acquired He-T DNA sequences. He-T DNA is a complex family of repeated sequences found in the telomeric and pericentric heterochromatin of D. melanogaster chromosomes. He-T DNA sequences are detected, at various levels, in the most distal band on the end of each polytene chromosome in all D. melanogaster stocks. To our knowledge, these sequences have never been detected within the euchromatic chromosomal regions in any stock. The strong correlation between He-T DNA sequences and telomeric regions suggests that He-T sequences may have a role in organizing or maintaining the ends of chromosomes. The association of He-T DNA with newly acquired telomeres in a formerly euchromatic region, polytene region 13, strengthens this correlation.