[Reassociation of interspersed moderate DNA repeats]

Reassociation kinetics of the fragments of DNA consisting of interspersed repetitive and non-repetitive nucleotide sequences is considered in this paper. Based on the model, suggested by Gavrilov and Mazo (Mol. biol., 11, 101 1977), which takes into account the random DNA shearing, both reassociation kinetics of the total DNA in the region corresponding to interspersed repeat reassociation and that of the isolated preparation of interspersed repetitive sequences are calculated. In both cases influence of the repeat length on the reassociation rate is demonstrated. The estimation of the repetition frequency of rare repeats from pigeon genome is specified using calculations performed.

[Metabolically stable classes of nuclear messenger-like RNA. I. Detection and molecular characterization]

Two discreet in size molecular classes of metabolically stable messenger-like RNA molecules with sedimentation coefficientes about 28S and 18S have been revealed in the nuclei of pigeon bone marrow cells. The structural pecularities of 28S RNA class were investigated more carefully. It was shown to constitute the largest fraction of nuclear messenger-like RNA and is characterized by a GC/AU ratio 1.13. As pulse-labeled nuclear RNA, 28S stable nuclear RNA hybridizes with the unique and rare repeated DNA, it does not contain poly(A)-sequences and is found in a form of RNP particles with density of 1.41 g/sm3, tightly bound to chromatin.

["Extracyclic" DNA synthesis and the accumulation of total protein and hemoglobin in erythroid series cells in anemia in pigeons]

Two types of biosynthetic processes associated with cytodifferentiation underlie the "reserve" erythropoiesis of pigeons during anemia: 1) cells rapidly increase their nuclear DNA amount up to the level of 4c, whereas the total protein remains at the initial level; furtheron, cells double also their protein amount, and then enter into the phase of differentiation and specialization; after having hemoglobin accumulation they divide; 2) a limited increase of DNA amount takes place up to the level not exceeding 130% of the initial level; in this case a synchronous increase of the hemoglobin amount is detected in the cell. The first type processes provide the accumulation of the specific product and the accelerated increase of the number of erythrocytes in the population. The second way is aimed only to the accumulation of the specific product in a greater amount.

[Poly(A)-containing RNA from germinating wheat embryos]

Rapidly labelled mRNAs were isolated from informosomes and polyribosomes of imbibed wheat embryos. The distribution of poly(A) sequences in these fractions were studied by poly(U) Sepharose chromatography. It was shown that informosomes contain 11% polyadenylated mRNA while polyribosomes--38%. This fact suggests the important role of poly(A) sequences for translation of mRNA.

[Role of serine-rich histone (H5) in bird erythrocyte genome inactivation]

The ability of H5 and H1 histones, purified from immature or mature pigeon erythroid cells, to suppress RNA synthesis in vitro was compared. It was found that H1 histones from both sources as well as histone H5 from bone marrow suppress RNA synthesis to a comparable degree while H5 from the mature erythrocytes exhibits significantly higher suppression efficiency. H5 histone subfractions, differing in phosphate content, also had different ability to restrict the template activity of chromatin: the higher is the phosphorylation level of H5 histone, the weaker is its effect on the transcription.

[Isolation and characteristics of 2 transcribing families of pigeon-genome repetitive sequences]

From pigeon DNA two families of repeats have been isolated: one (frequency of repetitions 30--40 times per haploid genome) actively transcribing and the second (frequency of repetitions 2000--2800 times) weakly transcribing in erythroid cells. The reassociation kinetics, GC-content and size of isolated repeats were investigated. Actively transcribing repeats (average length of 350 nucleotides) contain about 55% GC-nucleotides and alternate in the genome with AT-rich sequences of the unique type. Comparison of isolated families of repeats revealed differences in the structure and posttranscriptional fate of RNA transcribed from them.

[Role of integrity of the inner nuclear membrane in energy supply for protein synthesis in the isolated cell nuclei of the salivary glands of Chironomus plumosus]

Using isolated nuclei of salivary grand cells of Chironomus plumosus larvae, it was revealed that the integrity of nuclei was a necessary condition for realization of protein synthesis in the nuclei. The involvement of nuclear particles in the above synthesis is supposed.

[The problem of intranuclear protein synthesis]

This review deals with the analysis of the conflinting situations that appear during the study of the translational apparatus in cell nuclei. Experimental approaches used to unravel this problem are surveyed.