Identification of 10 nm non-chromatin filaments in the macronucleus ofEuplotes eurystomus

DNA Replication: An in vivo Space-Time Continuum in the Ciliate Replication Band

The replication band in the macronucleus of ciliated protozoa has fascinated microscopists since the 19^th Century. It migrates through the nucleus, corresponding to a region of DNA replication and nascent chromatin assembly. A new study shows that calcium and actin filaments may participate in the formation and migration of the replication band.

The Function and Evolution of Motile DNA Replication Systems in Ciliates

DNA replication is a ubiquitous and conserved cellular process. However, regulation of DNA replication is only understood in a small fraction of organisms that poorly represent the diversity of genetic systems in nature. Here we used computational and experimental approaches to examine the function and evolution of one such system, the replication band (RB) in spirotrich ciliates, which is a localized, motile hub that traverses the macronucleus while replicating DNA. We show that the RB can take unique forms in different species, from polar bands to a "replication envelope," where replication initiates at the nuclear periphery before advancing inward. Furthermore, we identify genes involved in cellular transport, including calcium transporters and cytoskeletal regulators, that are associated with the RB and may be involved in its function and translocation. These findings highlight the evolution and diversity of DNA replication systems and provide insights into the regulation of nuclear organization and processes.

Antibodies against Tetrahymena 14-nm filament-forming protein recognize the replication band in Euplotes

Tetrahymena 14-nm filament-forming protein (49K protein) is a structural protein which is involved in activity of the pronuclei during conjugation (O. Numata, T. Sugai, and Y. Watanabe (1985) Nature (London) 314, 192-194). Using monoclonal and polyclonal antibodies, we here demonstrate the presence of a cross-reactive protein (CRP-49) within the macronuclear replication bands of Euplotes harpa and E. eurystomus which is recognized by anti-49K protein antibodies. Immunoblotting reveals that both monoclonal and polyclonal antibodies cross-react to a protein with an apparent molecular mass of 50 kDa in an E. harpa cell extract and to a protein of 49 kDa in a macronuclear extract of E. eurystomus. The antibodies used in this study have no effect upon in vitro DNA synthesis in the replication band of E. eurystomus.