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 ver sions 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 fa te 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 pr ecursor DNA sequence are still retained in the mature macronucleus, th e modified macronuclear DNA sequence is correctly cut out from the vec tor, telomeres are added de novo and it is stably retained in the macr onucleus during vegetative growth of the cells, This vector system rep resents an experimental system that allows the identification of DNA s equences involved in the processing of macronuclear DNA sequences duri ng macronuclear development.