LOCALIZATION OF CENTROMERE FUNCTION IN A DROSOPHILA MINICHROMOSOME

The DNA elements responsible for centromere activity in a metazoan hav e been localized using the Drosophila minichromosome Dp1187. Deleted m inichromosomes were generated by irradiation mutagenesis, and their mo lecular structures were determined by pulsed-field Southern blot analy sis. Analyses of the transmission behavior of Dp1187 derivatives local ized sequences necessary for chromosome inheritance within the centric heterochromatin. The essential core of the centromere is contained wi thin a 220 kb region that includes significant amounts of complex DNA. Completely normal inheritance also requires similar to 200 kb on eith er side of the essential core. This flanking DNA predominantly contain s highly repeated sequences, and the amount required for normal transm ission differs among division types and between the sexes. We propose that the essential core is the site of kinetochore formation and that flanking DNA provides two functions: sister chromatid cohesion and ind irect assistance in kinetochore formation or function.