PDD1P, A NOVEL CHROMODOMAIN-CONTAINING PROTEIN, LINKS HETEROCHROMATINASSEMBLY AND DNA ELIMINATION IN TETRAHYMENA

During Tetrahymena conjugation, programmed DNA degradation occurs in t wo separate nuclei. Thousands of germline-specific deletion elements a re removed from the genome of the developing somatic macronucleus, and the old parental macronucleus is degraded by an apoptotic mechanism. An abundant polypeptide, Pdd1p (formerly p65), localizes to both of th ese nuclei at the time of DNA degradation. Here we report that, in dev eloping macronuclei, Pdd1p localizes to electron-dense, heterochromati c structures that contain germline-specific deletion elements. Pdd1p a lso associates with parental macronuclei during terminal stages of apo ptosis. Sequencing of the PDD1 gene reveals it to be a member of the c hromodomain family, suggesting a molecular link between heterochromati n assembly and programmed DNA degradation.