PROGRAMMED DNA DELETIONS IN TETRAHYMENA - MECHANISMS AND IMPLICATIONS

Ciliated protozoa carry, out remarkable DNA rearrangements during nucl ear differentiation, including precise deletion of thousands of specif ic DNA fragments from their somatic genomes. Recent molecular studies on DNA deletion in Tetrahymena have revealed two interesting sets of c is-acting regulatory sequences, one determines the general regions to be deleted and the other the precise end points of deletion. This info rmation suggested a novel mechanism of DNA rearrangement and raised in teresting questions regarding Us evolutionary origin It is speculated that this process might be related to the unique genetic property of c iliate macronuclei, which transcribe actively and divide without chrom osome condensation.