THE DROSOPHILA-MELANOGASTER-DODECASATELLITE SEQUENCE IS CLOSELY LINKED TO THE CENTROMERE AND CAN FORM CONNECTIONS BETWEEN SISTER CHROMATIDSDURING MITOSIS

We have used fluorescence in situ hybridisation to wild-type and rearr anged mitotic chromosomes to map the Drosophila melanogaster dodecasat ellite sequence. It is located at a unique site, within the pericentri c heterochromatin of the right arm of the third chromosome, closely li nked to the primary constriction. In polytene chromosomes, dodecasatel lite is found as one or a few dots in the central region of the chromo centre. In untreated diploid cells, dodecasatellite sequences are foun d as one or two dots throughout the cell cycle. This distribution can be altered in a cell cycle-dependent manner in two ways. Firstly, in i nterphase cells, hypotonic shock promotes the decondensation of the ge nomic region containing this satellite, resulting in a string-like str ucture. Secondly, some of the precociously separated sister chromatids produced by colchicine treatment show dodecasatellite within the inte rvening space connecting the main dodecasatellite signals of each chro matid. The distribution of dodecasatellite seems to be rather constant between individuals of the same species, as indicated by the lack of any detectable variations in its pattern amongst individuals from six geographically distant strains of D. melanogaster. On the other hand, the distribution of dodecasatellite shows a remarkable degree of varia tion amongst closely related species of the melanogaster subgroup rang ing from a non-detectable signal in Drosophila yakuba and Drosophila t eissieri, to staining in the X, second and third chromososomes of Dros ophila mauritiana.