The Molecular Nature of the Toromere inDrosophila LummeiHackman and its role in Chromosome Behavior

Open Access
Publisher Website
Google Scholar
Abstract
The toromere previously found by other workers in the distal end of the sixth chromosome (microchromosome) of D. limmei was studied using differential staining of Drosophila lummei giant chromosomes. The toromere which was first described as a quinacrine-bright structure appears as a C-positive body. Quantitative cytofluorometric analysis showed highly significant increase in toromeric DNA under low temperature conditions. In situ hybridization of 125I nick-translated D. virilis sDNA (all three satellites were included in the sample) with polytene chromosomes of D. lummei larvae cultured at 12° C revealed no label incorporation into toromere region. However in situ hybridization of 3H-RNA complementary to highly repetitious DNA of D. lummei and D. virilis (Cot = 10−1–10−2) with polytene chromosomes of the larvae cultured at 12° C coupled with banding studies enable us to conclude that the toromere probably contains an AT-rich repeated DNA. A well-developed toromere in the sixth chromosome of D. lummei was also demonstrated at normal temperature (25° C) in interspecific hybrids. The role of the toromere structure in the mitotic behavior of microchromosomes and their replication pattern is discussed.