TELOMERIC INTERACTIONS RESULT IN THE FORMATION OF INTRAMOLECULAR CIRCLES BEHAVING AS TOPOLOGICALLY CONSTRAINED

The gene-sized macronuclear DNA molecules of hypotrichous ciliates car ry telomeric sequences of homogenous length. Incubation of these molec ules at low concentrations in the presence of monovalent cations (K+, Na+, Cs+) leads to the formation of intramolecular circles. They can b e visualized on one or two-dimensional agarose gels only when KCl is p resent in the gel. From their electrophoretic behavior on agarose gels as well as on density gradients it can be concluded that they are top ologically constrained. Digestion of macronuclear DNA with S-1 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 interactio ns. Several models of these interactions are discussed. (C) 1998 Acade mic Press.