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A screening of new synthetic opioid-like peptides has been carried out by the radioreceptor assay using selective labeled ligands to mu-, delta- and gamma-opioid receptors of the rat brain membranes. With this aim peptides from sequences of the following proteins were used: kapporphin-Tyr-Ser-Phe-Gly-Gly and its analogues-Tyr-Ser-Phe-Gly-Gly-NH2, Tyr-D-Ser-Phe-Gly-Gly, Tyr-D-Ser-Phe-Gly-Gly-NH2, myelorphin-Phe-Gly-Tyr-Gly-Gly, interenkephalin B-Arg-Arg-Gln-Phe-Lys and chimeric peptide IEPhBin 1-Tyr-Gly-Gly-Phe-Leu-Arg-Pro-Tyr-Ile-Leu consisting of leu-enkephalin and pentaneurotensin. It has been found that myelorphin has a prevalent affinity to mu-receptor, while the kapporphin analogues both to mu- and delta-receptors. The presence of pentaneurotensin in chimeric peptide does not affect the specificity of binding to opioid receptors, but decreases affinity to mu- and delta-receptors approximately by an order as compared to leu-enkephalin. Kapprorphin and interenkephalin B displace neither of the selective labeled opioid ligands under study.

The nuclei of spleen lymphocytes showed nuclease activity becoming manifest under conditions optimal for different types of DNA-ase (DNA-ase I, DNA-ase II, micrococcal nuclease and Ca, Mg-dependent endonuclease). No diversity of nuclease activity was found in the liver or kidney nuclei. A high nuclease activity in the lymphocyte nuclei provides for a deeper endonucleolysis of the lymphocyte chromatin as compared to that in the liver nuclei. The variety of nucleic activity and more advanced chromatin endonucleolysis in the spleen lymphocyte nuclei may be associated with rapid cell renewal of the lymphocyte pool in lymphoid organs and with necessity for autolysis of degraded lymphocyte genome. It may also ensure the somatomutagenic mechanism of diverse V-genes and of V- and C-gene combination.

Biochemical assay of the length of the element of the highest level of compactization of deoxyribonucleoprotein fibril, i.e. the loop, in interphasic chromosomes of the liver of some animals (rat, cat, hen, pigeon, tortoise, frog) reveals significant variation of the magnitude of this value. The smallest length of the loop among the organisms investigated was found in tortoise chromosomes--5--6 X 10(3) nucleotide pairs. The length of the loop structures in mammalian chromosomes (rats, cats) is equal to 45-75 X 10(3) nucleotide pairs. In birds and amphibians, chromosomes exhibit an intermediate size of the loop element as compared to chromosomes from mammals and reptiles. Possible connection between the length of the loop structures and chromosomal diameter is discussed together with the "anomalous" size of chromosomal loops in the frog.

Different histone fractions contain sequences homologous to those of several regulatory peptides. All the histone fractions demonstrated dose-dependent positive chronotropic effect in spontaneously contracting rat atrial preparations. The range of their activity was as follows: H4 greater than H1 greater than H2a much greater than H3. Synthetic COOH-terminal histone H4 pentapeptide (historphin) Tyr-Gly-Phe-Gly-Gly demonstrated opioid activity by inhibiting electrostimulated guinea-pig ileal contractions. It is suggested that some biological activities of histones are related to the presence of regulatory peptide sequences in their structure.

Isolated nuclei from rat liver were incubated at different time intervals under conditions, optimal for manifestation of the Ca, Mg-dependent endonuclease activity. After each of the 6 endonucleolyses chromatin was extracted and 6 chromatin fractions (I--VI) and "residual" chromatin were collected. A comparative analysis of the "early" (I--III) and "late" chromatin fractions revealed an increased RNA content in the "late" fractions and changes in the composition of the non-histone proteins. Electrophoresis in acrylamide gel concentration gradient demonstrated that fractions I--III predominantly contain high molecular weight fragments whereas fractions IV-VI are represented by highly fragmented chromatin. Each fraction was characterized by peculiar shapes of alkaline denaturation curves and by heterogeneity of charges of their constituent chromatin fragments.

Rat liver chromatin fragments obtained after the chromatin digestion with Ca,Mg-dependent intranuclear endonuclease were studied using electrophoresis in polyacrylamide gel concentration gradient. It is found that the content of large chromatin fragments decreases in the presence of exogenous RNAse. Possible structural role of RNA in the chramatin organization is discussed.

The oligomer chromatin fragments relatively uniform in size (8--11 nucleosomes) were prepared by a short-term endonycleolysis. The heterogeneity of these fragments with respect to their electrophoretic mobility was revealed using free flow electrophoresis. The individual fragmentated chromatin subfractions were obtained. These subfractions differed in their protein and RNA content per DNA weight unit, in quantitative ratios of different zones of high molecular weight non-histone proteins and in thermal and alkaline denaturation kinetics. It was also found that the parameters investigated are correlated with electronegativeity of the fragmentated chromatin subfractions.

Using polyacrylamide gel electrophoresis, the composition of cationic chromosomal proteins of the cells with completely blocked genome (crayfish, triton and frog spermatozoa, bird erythrocytes, rabbit and cow neutrophils) and homologous somatic cells with matrix-active genome was studied. It was shown that the most common feature of the composition of these cationic chromosomal proteins is the presence of several subfractions of histone H1. This is probably due to the necessity of total condensation of chromosomal fibrills.

The analysis of chromatin fragments from liver, kidney, spleen and brain by means of electrophoresis in polyacrylamide gel concentration gradient has revealed the organospecificity of the chromatin fragmentation with endonucleases. The highest endonucleolysis of chromatin was observed in spleen nuclei, it was moderate in kidney and liver and it was practically absent in brain. Differences in endonucleolysis of the organs studied demonstrate their correlation with the mitotic activity.

The binding of the antibiotic dyes to chromatin fragmented by various ways and to preparations of "complete" (MH3, 206 DNA base pairs) and "minor" MH1, 155 DNA base pairs) nucleosomes was studied. The latter were obtained from the total hydrolysate of nuclear chromatin hydrolysis by Ca-Mg-dependent endonuclease, using preparative electrophoresis in polyacrylamide gel. In liver chromatin of different vertebrate species the actinomycin D binding is decreased by 70% as compared to DNA binding, while that of ethidium bromide is reduced only by 40%. The splitting of part of internucleosomal DNA by Ca-Mg-dependent endonuclease further decreases the number of binding sites for ethidium bromide, but not for actinomycin D. MH3 bid 24 molecules of actinomycin D per 10(3) of nucleotides; their DNA contain 43.4% of GC-pairs. The GC content in MH1 is 47.7%; they bind 28 dye molecules per 10(3) of nucleotides. The data obtained are discussed in terms of possible predominant localization of nucleosomal cores in GC-pair-rich DNA sites.