UBCD1, A DROSOPHILA UBIQUITIN-CONJUGATING ENZYME REQUIRED FOR PROPER TELOMERE BEHAVIOR

The end-to-end association of chromosomes through their telomeres has been observed in normal cells of certain organisms, as well as in sene scent and tumor cells. The molecular mechanisms underlying this phenom enon are currently unknown. We show here that five independent mutant alleles in the Drosophila UbcD1 gene cause frequent telomere-telomere attachments during both mitosis and male meiosis that are not seen in wild type. These telomeric associations involve all the telomeres of t he D. melanogaster chromosome complement, albeit with different freque ncies. The pattern of telomeric associations observed in UbcD1 mutants suggests strongly that the interphase chromosomes of wild-type larval brain cells maintain a Rabl orientation within the nucleus, with the telomeres and centromeres segregated to opposite sides of the nucleus. The UbcD1 gene encodes a class I ubiquitin-conjugating (E2) enzyme. T his indicates that ubiquitin-mediated proteolysis is normally needed t o ensure proper telomere behavior during Drosophila cell division. We therefore suggest that at least one of the targets of UbcD1 ubiquitina tion is a telomere-associated polypeptide that may help maintain prope r chromosomal orientation during interphase.