[Increase in the quantity of highly repetitive sequences in extrachromosomal circular DNAs under inhibition of translation by cycloheximide]. / Uvelichenie soderzhaniia vysokopovtoriaiushchikhsia posledovatel'nostei v ékstrakhromosomnykh kol'tsevykh DNK pri tormozhenii transliatsii tsiklogeksimidom.

Small polydispersed circular DNA(spcDNA) was isolated from cultivated HeLa cells. Cells were treated by cycloheximide in concentrations of 1 and 50 micrograms/ml. Gradient fractions were dot blotted to nitrocellulose filters and were hybridized with different repetitive DNAs. The pool of repetitive DNA sequences in fraction of spcDNA increased for cycloheximide treated cells. The content of Alu sequences increased by 1.5-2.5 times, "classical" satellite DNA--by 5-7 times, alpha-satellite--by 3-5 times.

[Binding of SSB-protein from Ehrlich ascites carcinoma cells with DNA and polyribonucleotides]. / Sviazyvanie SSB-belka iz kletok astsitnoi kartsinomy érlikha s DNK i poliribonukleotidami.

Binding of SSB-protein from Ehrlich ascites tumor to ssDNA from M13 phage leads to its compactization. The structure of the complex at the protein/DNA ratios far from the saturation level looks like "beads-on the string". DNA that was fully saturated with protein forms collapsed globular structure. Binding of the protein to the dsDNA from phage lambda increases its flexibility and decreases the coil dimensions; no "beads-on the string" structure are seen. The protein possess slight destabilizing effect on hairpin helices of M13DNA. Competition studies demonstrate that the binding properties of protein with polyribonucleotide lattices and DNA's decrease in ranking as follows: poly(rG) greater than or equal to poly(rI) greater than or equal to ssDNA greater than dsDNA greater than poly(rA) congruent to approximately poly(rU). Thus SSB-protein from Ehrlich ascites tumor differs significantly from its presumed prokaryotic analogs.

[Comparative analysis of the structure of double-stranded RNA from killer strains of Saccharomyces cerevisiae]. / Sravnitel'nyi analiz stroeniia dvuspiral'nykh RNK killernykh shtammov Saccharomyces cerevisiae.

Double-stranded RNAs (M and L molecules) of two strains of the killer system Saccharomyces cerevisiae M437 (wild type) and ski-5 (superkiller mutant) were studied by means of electron microscopy and high resolution thermal melting. The M molecules of the ski-5 mutant were by 100 b.p. shorter than those of M437. L molecules were of the same length for both strains. Analysis of the differential melting curves of L molecules showed that L molecules differ significantly in their nucleotide sequences, whereas M molecules were practically identical. It was found that M molecules contained a long AU region: that of M molecules of M 437 was 170-180 b.p. long and contained almost no GC pairs, whereas the AU region of M molecules of the ski-5 mutant was three times shorter and contained GC pairs.

[The region of phage T4 W-29 genes: cloning and expression]. / Oblast' genov W-29 faga T4: klonirovanie i ékspressiia.

The EcoRI fragment of T4 DNA containing the W-29 genes and its subfragments were cloned in the pBR322 and the singlestranded M13 phage. Hybridization with a cloned DNA showed that in T4 infected cells the transcription of the late genes 25-29 depends on the phage-induced RNA polymerase changes and on replication of phage DNA. At a late infection stage one also observes an enhanced transcription of the (early) genes uvsW and uvsY, which depends on viral DNA replication. Both early and late genes within recombinant plasmids are also expressed in uninfected cells carrying a plasmid regardless of the inserted fragment orientation and independently of the vector promoters. Hybrid plasmids demonstrated a high frequency of recombination with phage DNA in the infected cell. An RNA polymerase from uninfected cells binds itself to the late cloned genes to form "open" complexes. A purified RNA polymerase transcribes both early and late genes within recombinant plasmids. The relative transcription of the late cloned genes is enhanced if one uses an RNA polymerase from T4-infected cells. The super-helicity of template DNA is essential for transcription of early and late genes.

[Dibromoethylacetate - a new agent for fixing the unwound regions of DNA. Denaturation maps of mitochondrial DNA from the rat liver]. / Dibrométilatsetat - novyi agent dlia fiksatsii despiralizovannykh uchastkov DNK. Denaturatsionnaia karta mitokhondrial'noi DNK pecheni krysy.

On the basis of the reaction of dibromoethylacetate with adenine and cytosine at the uncoiled regions of DNA it was possible to fix these molten regions (the degree of denaturation was about 16%) for rat liver mitochondrial DNA. Modification of all accessible adenine and cytosine residues in 0.14 M Na-acetate, pH 5.65, was completed at 70-80 degrees C in 15-20 min. Using the computer orientation for the set of fixed BamHI-fragments and the linear molecules of full length the denaturation map of mtDNA was constructed, the GC-content of the molten regions was about 28%. The dibromoethylacetate is a perspective agent for screening DNA with a low content of destabilizing regions (for instance, DNA of malignant cells).