Figure 7.

Model for DNA processing during macronuclear development in hypotrichous ciliates. Inverted repeats acting as cis-acting DNA sequences required for DNA processing are localized in both subtelomeric regions but not necessarily at similar positions. By interaction of these sequences, a loop-like structure is formed, which is then resolved on its base by a specific nuclease. This implies that a precise cut is made only at the 3' end, the 5' end has to be filled in by a so far unknown proofreading mechanism. Telomeric sequences are then added de novo.