A nuclear protein involved in apoptotic-like DNA degradation in Stylonychia: Implications for similar mechanisms in differentiating and starved cells

Ciliates are unicellular eukaryotic organisms containing two types of nucle i: macronuclei and micronuclei. After the sexual pathway takes place, a new macronucleus is formed from a zygote nucleus, whereas the old macronucleus is degraded and resorbed. In the course of macronuclear differentiation, p olytene chromosomes are synthesized that become degraded again after some h ours. Most of the DNA is eliminated, and the remaining DNA is fragmented in to small DNA molecules that are amplified to a high copy number in the new macronucleus. The protein Pdd1p (programmed DNA degradation protein 1) from Tetrahymenn has been shown to be present in macronuclear anlagen in the DN A degradation stage and also in the old macronuclei, which are resorbed dur ing the formation of the new macronucleus. In this study the identification and localization of a Pdd1p homologous protein in Stylonychia (Spdd1p) is described. Spdd1p is localized in the precursor nuclei in the DNA eliminati on stage and in the old macronuclei during their degradation, but also in m acronuclei and micronuclei of starved cells. Ln all of these nuclei, apopto tic-like DNA breakdown was detected. These data suggest that Spdd1p is a ge neral factor involved in programmed DNA degradation in Stylonychia.