Telomeric interactions result in the formation of intramolecular circles behaving as topologically constrained

The gene-sized macronuclear DNA molecules of hypotrichous ciliates carry telomeric sequences of homogenous length. Incubation of these molecules at low concentrations in the presence of monovalent cations (K+, Na+, Cs+) leads to the formation of intramolecular circles. They can be visualized on one or two-dimensional agarose gels only when KCl is present in the gel. From their electrophoretic behavior on agarose gels as well as on density gradients it can be concluded that they are topologically constrained. Digestion of macronuclear DNA with S1 as well as various exonucleases indicate that both the 3' overhang and the 5' C-rich strand of the telomeric repeat is involved in these interactions. Several models of these interactions are discussed.