[Molecular genome organization in ciliates].

The review summarizes modern views on to the structure and differentiation of the nuclear apparatus in ciliates. The genetic system of ciliates (type Ciliophora) includes two types of nuclei: germinal micronucleus (MIC) and somatic macronucleus (MAC). The MAC development is associated with the rearrangement of the MIC genome, which includes chromosome fragmentation and chromatin diminution. The loss of DNA constitutes from 10-15% (Tetrahymena termophila) to 95-98% of the genome in spirotrichs (Stylonychia, Oxytricha, and Euplotes). Analysis of molecular mechanisms underlying nuclear dualism in ciliates promoted radical revision of the concept on the interactions and roles of MAC and MIC. The micronucleus, as an inactive element, is an ideal field for the invasion and further expansion of mobile genetic elements. Chromatin diminution plays the purifying role, restoring the native genome structure. The process of recognition of "genetic garbage" to be eliminated has many features in common with the siRNA-mediated heterochromatization. The presence of this mechanism in very early radiated eukaryotic lineages (Opistokonta and Chromalveolata), indicates that it arose at the earliest stages of the eukaryotic evolution, probably, as a mechanism promoting genome integrity and stability.

[Comparative description of macronuclear electrophoretic karyotypes of Paramecium primaurelia and Paramecium novaurelia sibling species].

The macronuclear genomes of two sibling species belonging to the Paramecium aurelia complex--P. primaurelia and P. novaurelia--were analyzed by pulsed-field gel electrophoresis (PFGE). Their electrophoretic karyotypes showed a continuous spectrum of different-sized DNA molecules with a species-specific pattern of banding, which was reproducible and did not change with strain senescence. Thus, P. aurelia macronuclear PFGE profiles could be described by an approach analogous to that used for the description of metaphase chromosome banding patterns. At first, well-identifiable regions (size fractions) of a PFGE profile, which can be seen at any resolution, are determined. Then, the bands of the second order of resolution (subfractions) can be defined in some of these regions. The blocks of the first and second orders can be utilized as inner markers of the PFGE profile allowing precise comparison of different PFGE profiles. Such comparative analysis has demonstrated some marking differences in organization of the macronuclear genomes of P. primaurelia and P. novaurelia, and low level of intraspecific polymorphism. Worth noting is that the P. novaurelia strain isolated in USA was different from all other analyzed P. novaurelia strains originating from Europe. The nature of banding of P. aurelia PFGE profiles is discussed. The revealed high order and stability of the macronuclear genome organization makes possible searching for new approaches to study the mechanisms of this non-trivial genome formation and maintenance. Further PFGE analysis of the macronuclear genomes of the other Paramecium species in relation with the Paramecium phylogeny may provide insights into the directions of the evolution of the macronuclear genome in Ciliata.

[Identification of Chlorella viruses in Paramecium bursaria clones by pulse-field electrophoresis].

The ciliates Paramecium bursaria contain endosymbiotic green algae Chlorella spp. in their cytoplasm. The algae isolated from P. bursaria are sensitive to large DNA-containing viruses of the family Phycodnaviridae. The type virus of this family is PBCV-1 (Paramecium bursaria Chlorella virus). Investigation of the total DNA of P. bursaria clones by pulse-field electrophoresis (PEP) revealed a pronounced band on PEP profiles of some P. bursaria clones; the band was formed by DNA molecules of approx. 300 kb. This band probably contained the DNA of chlorella virus. Two approaches were used in the present work to confirm this hypothesis. Microbiological tests were used to scan a collection of P. bursaria clones for specific types of viruses; the 300-kb band was revealed only in the PEP profiles of virus-containing clones. Blot hybridization of P. bursaria total DNA separated by pulse-field electrophoresis with the virus-specific probe revealed that the band under study contained the DNA of a chlorella virus. Paramecium clones were shown to contain approx. 10(5) copies of nonintegrated viral DNA.

[Determination of the minimum size of Gallus gallus domesticus chicken microchromosome by a pulse electrophoresis method]. / Opredelenie minimal'nogo razmera mikrokhromosom kuritsy Gallus gallus domesticus metodom pul's-élektroforeza.

The karyotype of the chicken Gallus gallus domesticus was studied by means of pulsed-field electrophoresis. An electrokaryogram was obtained for the microchromosomal (MI) portion of the chicken genome. Chicken MIs were separated into two fractions. A fraction with a higher mobility included MIs sized 3.4-4.8 Mb; the lower size limit of a less mobile fraction corresponded to MIs of approximately 5 Mb. The smallest MI in the chicken karyotype was estimated at 3.4 +/- 0.25 Mb.

[Symbiotic bacteria of the macronucleus of Paramecium caudatum]. / Simbioticheskie bakterii makronukleusa infuzorii Paramecium caudatum

Particles of a newly described endosymbiont of Paramecium caudatum, clone M-115, here referred to as iota--particles, are Gram--negative bacteria. The symbionts are only present within macronuclei and not in the cytoplasm or in the micronuclei. The cells of clone M-115 iota do not display any killer-effect when mixed with "clean" cultures of Paramecia. In life cycle of the symbiont, there is an alternation of two morphological forms: a spindle-shaped form 2.0--2.5 microns long and a rod-shaped form -- about 18 microns long. The data obtained revealed a high ability to infect cell of "clean" clones of P. caudatum with iota-particles. The antagonistic relationships between two different species of endonucleosymbionts: iota- and omega-particles, are detected. The revealed biological features of iota can be used for studying the mechanisms of nuclear differentiation in ciliates.