[Stabilization of chromonema--one of the highest compactization levels--by visible light in the presence of ethidium bromide].

: This paper deals with the ultrastructure and behavior of interphase chromatin and metaphase chromosomes of L-197 culture cells under experimental conditions, which help to reveal the chromonemal level of chromosomal structure after the treatment of living cells with 0.1% Triton X-100 and 3 mM CaCl2. In these conditions, the chromonemata can be seen as dense chromatin fibers with thickness about 100 nm. Such chromosomes, whose chromonemal substructure after the treatment with hypotonic solution (10 mM Tris-HCl), look like loose chromosomal bodies composed of elementary 30 nm DNP fibrils. On the other hand, if chromosomes, in which chromonemal levels were revealed by 3 mM CaCl2, were treated with etidium bromide and then illuminated by light with length wave about 460 nm, no chromosomal decondensation in hypotonic conditions is observed. Chromonemata in chromosomes stabilized by light retain their density and dimensions. It is very important that chromonemata in stabilizated chromatin of metaphase chromosome keep specific connections between themselves and also general trend in their composition inside the chromosome. Thus, we have found conditions for observation of chromonemal elements in metaphase chromosome, providing the possibility for future three-dimensional investigation of chromonema packing in mitotic chromosomes.