A subtelomeric DNA sequence is required for correct processing of the macronuclear DNA sequences during macronuclear development in the hypotrichous ciliate Stylonychia lemnae

During macronuclear differentiation in ciliated protozoa a series of progra med DNA reorganization processes occur. These include the elimination of mi cronuclear-specific DNA sequences, the specific fragmentation of the genome into small gene-sized DNA molecules, the de novo addition of telomeric seq uences to these DNA molecules and the specific amplification of the remaini ng DNA molecules. Recently we constructed a vector containing the modified micronuclear version of macronuclear destined DNA sequences that was correc tly fragmented and telomeres were added de novo after injection into the de veloping macronucleus, It therefore must contain all the cis-acting sequenc es required for these processes. We made a series of vectors deleting diffe rent sequences from the original vector. It could be shown that at least in the case studied here no micronuclear-specific sequences are required for specific fragmentation of the genome and telomere addition. However, a shor t subtelomeric sequence at the 3'-end is essential for these processes, whe reas no specific cut seems to occur at the 5'-end. In addition, we can show that the processing activity is restricted to a short period of time durin g macronuclear differentiation and that a preceding transcription is requir ed for correct processing of macronuclear-destined DNA sequences. Possible mechanisms of these processes will be discussed.