STYLONYCHIA LEMNAE AS A MODEL ORGANISM FOR STUDIES OF MACRONUCLEAR MINICHROMOSOMES OF THE CILIATES
A. Yu. Pimenov, I. B. Raikel, I. N. Skovorodkin, Yu. I. Podlipaeva, D. Ammermann,
S. O. Skarlato 1
Institute of Cytology RAS, St. Petersburg;
1 e-mail: sergei_skarlato@yahoo.com
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 α1- and α2-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.
Key words: ciliates, macronucleus, minichromosomes of lower eukaryotes, nuclear apparatus
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