The processing of macronuclear-destined DNA sequences microinjected into the macronuclear anlagen of the hypotrichous ciliate Stylonchia lemnae.

We describe the construction of a vector carrying the micronuclear versions of two macronuclear DNA molecules, one of which was modified by the insertion of a polylinker sequence. This vector was injected into the polytene chromosomes of the developing macronucleus of Stylonychia and its processing during further macronuclear development and its fate in the mature macronucleus were analyzed. In up to 30% of injected cells the modified macronuclear DNA sequence could be detected. While the internal eliminated sequences (IES) present in the macronuclear precursor DNA sequence are still retained in the mature macronucleus, the modified macronuclear DNA sequence is correctly cut out from the vector, telomeres are added de novo and it is stably retained in the macronucleus during vegetative growth of the cells. This vector system represents an experimental system that allows the identification of DNA sequences involved in the processing of macronuclear DNA sequences during macronuclear development.