[Stylonychia lemnae as a model organism for studies of macronuclear minichromosomes of the ciliates].

The unique structural and functional organization of macronuclear (somatic nucleus) genome of the spirotrichous ciliates, exemplified by Stylonychia lemnae, has been reviewed. Data on the architecture of S. lemnae nuclear apparatus at interphase and during vegetative cell division, conjugation or autogamy are summarized. Special attention being paid to the structural and functional peculiarities of short macronuclear minichromosomes known to contain protein-coding regions, 5'- and 3'-flanking nontranslated regions, and telomeres. A hypothesis, previously put forward, according to which in the spirotrichous ciliates the telomeres themselves may serve as starting points of replication in minichromosomes, has now received its further substantiation. The recent experimental data, which confirm that 5'-nontranscribed DNA leader sequence of alpha1- and alpha2-tubulin-encoding minichromosomes display at least several regulatory elements typical for eukaryote promoter (TATA-box, CAAT-box, transcriptional initiator), are discussed. Up to now, there is no confirmation with regard to a possible existence in the spirotrichous minichromosomes of specific regulatory sequences capable of controlling both replication and transcription processes.