Short Exogenous Peptides Regulate Expression of CLE, KNOX1, and GRF Family Genes in Nicotiana tabacum.

Exogenous short biologically active peptides epitalon (Ala-Glu-Asp-Gly), bronchogen (Ala-Glu-Asp-Leu), and vilon (Lys-Glu) at concentrations 10-7-10-9 M significantly influence growth, development, and differentiation of tobacco (Nicotiana tabacum) callus cultures. Epitalon and bronchogen, in particular, both increase growth of calluses and stimulate formation and growth of leaves in plant regenerants. Because the regulatory activity of the short peptides appears at low peptide concentrations, their action to some extent is like that of the activity of phytohormones, and it seems to have signaling character and epigenetic nature. The investigated peptides modulate in tobacco cells the expression of genes including genes responsible for tissue formation and cell differentiation. These peptides differently modulate expression of CLE family genes coding for known endogenous regulatory peptides, the KNOX1 genes (transcription factor genes) and GRF (growth regulatory factor) genes coding for respective DNA-binding proteins such as topoisomerases, nucleases, and others. Thus, at the level of transcription, plants have a system of short peptide regulation of formation of long-known peptide regulators of growth and development. The peptides studied here may be related to a new generation of plant growth regulators. They can be used in the experimental botany, plant molecular biology, biotechnology, and practical agronomy.

Regulatory Peptides in Plants.

Many different peptides regulating cell differentiation, growth, and development are found in plants. Peptides participate in regulation of plant ontogenesis starting from pollination, pollen tube growth, and the very early stages of embryogenesis, including formation of embryo and endosperm. They direct differentiation of meristematic stem cells, formation of tissues and individual organs, take part in regulation of aging, fruit maturation, and abscission of plant parts associated with apoptosis. Biological activity of peptides is observed at very low concentrations, and it has mainly signal nature and hormonal character. "Mature" peptides appear mainly due to processing of protein precursors with (or without) additional enzymatic modifications. Plant peptides differ in origin, structure, and functional properties. Their specific action is due to binding with respective receptors and interactions with various proteins and other factors. Peptides can also regulate physiological functions by direct peptide-protein interactions. Peptide action is coordinated with the action of known phytohormones (auxins, cytokinins, and others); thus, peptides control phytohormonal signal pathways.

[Dnmt2 is the Most Evolutionary Conserved and Enigmatic Cytosine DNA Methyltransferase in Eukaryotes].

Dnmt2 is the most strongly conserved cytosine DNA methyltransferase in eukaryotes. It has been found in all organisms possessing methyltransferases of the Dnmt1 and Dnmt3 families, whereas in many others Dnmt2 is the sole cytosine DNA methyltransferase. The Dnmt2 molecule contains all conserved motifs of cytosine DNA methyltransferases. It forms 3D complexes with DNA very similar to those of bacterial DNA methyltransferases and performs cytosine methylation by a catalytic mechanism common to all cytosine DNA methyltransferases. Catalytic activity of the purified Dnmt2 with DNA substrates is very low and could hardly be detected in direct biochemical assays. Dnmt2 is the sole cytosine DNA methyltransferase in Drosophila and other dipteran insects. Its overexpression as a transgene leads to DNA hypermethylation in all sequence contexts and to an extended life span. On the contrary, a null-mutation of the Dnmt2 gene leads to a diminished life span, though no evident anomalies in development are observed. Dnmt2 is also the sole cytosine DNA methyltransferase in several protists. Similar to Drosophila these protists have a very low level of DNA methylation. Some limited genome compartments, such as transposable sequences, are probably the methylation targets in these organisms. Dnmt2 does not participate in genome methylation in mammals, but seems to be an RNA methyltransferase modifying the 38th cytosine residue in anticodon loop of certain tRNAs. This modification enhances stability of tRNAs, especially in stressful conditions. Dnmt2 is the only enzyme known to perform RNA methylation by a catalytic mechanism characteristic of DNA methyltransferases. The Dnmt2 activity has been shown in mice to be necessary for paramutation establishment, though the precise mechanisms of its participation in this form of epigenetic heredity are unknown. It seems likely, that either of the two Dnmt2 activities could become a predominant one during the evolution of different species. The high level of the Dnmt2 evolutionary conservation proves its activity to have a significant adaptive value in natural environment.

Plant DNA Methyltransferase Genes: Multiplicity, Expression, Methylation Patterns.

Expression and methylation patterns of genes encoding DNA methyltransferases and their functionally related proteins were studied in organs of Arabidopsis thaliana plants. Genes coding for the major maintenance-type DNA methyltransferases, MET1 and CMT3, and the major de novo-type DNA methyltransferase, DRM2, are actively expressed in all organs. Similar constitutively active expression was observed for genes encoding their functionally related proteins, a histone H3K9 methyltransferase KYP and a catalytically non-active protein DRM3. Expression of the MET1 and CMT3 genes is significantly lower in developing endosperm compared with embryo. Vice versa, expression of the MET2a, MET2b, MET3, and CMT2 genes in endosperm is much more active compared with embryo. A special maintenance DNA methylation system seems to operate in endosperm. The DNMT2 and N6AMT genes encoding putative methyltransferases are constitutively expressed at low levels. CMT1 and DRM1 genes are expressed rather weakly in all investigated organs. Most of the studied genes have methylation patterns conforming to the "body-methylated gene" prototype. A peculiar feature of the MET family genes is methylation at all three possible site types (CG, CHG, and CHH). The most weakly expressed among genes of their respective families, CMT1 and DRM1, are practically unmethylated. The MET3 and N6AMT genes have unusual methylation patterns, promoter region, and most of the gene body devoid of any methylation, and the 3'-end proximal part of the gene body is highly methylated.

Aging Epigenetics: Accumulation of Errors or Realization of a Specific Program?

Aging in mammals is known to be accompanied by a progressive loss of methylated cytosines from DNA. This loss is tissue-specific to a certain extent and affects mainly repeated sequences, transposable elements, and intergenic genome parts. Age-dependent DNA hypomethylation is correlated with and perhaps partly caused by a diminished activity of DNA methyltransferases. Along with the global DNA demethylation during aging, hypermethylation of certain genes occurs. On the whole-genome scale, an age-dependent hypermethylation is typical for genes associated with promoter CG islands, whereas hypomethylation mostly affects CG-poor genes, besides the repeated sequences, transposable elements, and intergenic genome parts mentioned above. The methylation levels of certain CG sites display strict correlation to age and thus could be used as a molecular marker to predict biological age of cells, tissues, and organisms. Epigenetic cell reprogramming, such as induced pluripotent stem cell production, leads to complete resetting of their epigenetic age.

[Epigenetic mutagenesis as program of age-related protein dysfunction and aging].

DNA methylation plays an important polyfunctional role in ontogenesis of human and mammals. A steep rise in probability of mutational substitution of CpG dinucleotide on TpG dinucleotide in the genome is one of the consequences of DNA methylation. All spectrum (17) of possible DNA and protein mutations caused by CpG-dinucleotide methylation in DNA were characterized, and the three most dangerous mutations (able to result in protein inactivation) were isolated. The computer program that allows one to predict all most probable mutations in the analyzed gene and encoded protein was created. On the example of genes from humans and various mammals, it was demonstrated that the amount of potentially dangerous sites of epigenetic mutagenesis in exons was drastically decreased as a result of genome evolution. But, at the same time, unforced preservation of such sites and their persistence were established, indicating the occurrence of age-related protein dysfunction built into the genome epigenetic program, resulting in apoptosis and aging; this program is based on the set and position of methylated codons in exonic gene regions. It is assumed that the program of epigenetic mutagenesis limits the lifetime of an individual, accelerating the deliverance of the population from long-lived individuals that completed the reproductive period.

Epigenetic mechanisms of peptidergic regulation of gene expression during aging of human cells.

Expression levels of genes encoding specific transcription factors and other functionally important proteins vary upon aging of pancreatic and bronchial epithelium cell cultures. The peptides KEDW and AEDL tissue-specifically affect gene expression in pancreatic and bronchial cell cultures, respectively. It is established in this work that the DNA methylation patterns of the PDX1, PAX6, NGN3, NKX2-1, and SCGB1A1 gene promoter regions change upon aging in pancreatic and bronchial cell cultures in correlation with variations in their expression levels. Thus, stable changes in gene expression upon aging of cell cultures could be caused by changes in their promoter methylation patterns. The methylation patterns of the PAX4 gene in pancreatic cells as well as those of the FOXA1, SCGB3A2, and SFTPA1 genes in bronchial cells do not change upon aging and are unaffected by peptides, whereas their expression levels change in both cases. The promoter region of the FOXA2 gene in pancreatic cells contains a small number of methylated CpG sites, their methylation levels being affected by cell culture aging and KEDW, though without any correlation with gene expression levels. The promoter region of the FOXA2 gene is completely unmethylated in bronchial cells irrespective of cell culture age and AEDL action. Changes in promoter methylation might be the cause of age- and peptide-induced variations in expression levels of the PDX1, PAX6, and NGN3 genes in pancreatic cells and NKX2-1 and SCGB1A1 genes in bronchial cells. Expression levels of the PAX4 and FOXA2 genes in pancreatic cells and FOXA1, FOXA2, SCGB3A2, and SFTPA1 genes in bronchial cells seem to be controlled by some other mechanisms.

Peptide regulation of gene expression and protein synthesis in bronchial epithelium.

INTRODUCTION: Some studies have shown that peptides have high treatment potential due to their biological activity, harmlessness, and tissue-specific action. Tetrapeptide Ala-Asp-Glu-Leu (ADEL) was effective on models of acute bacterial lung inflammation, fibrosis, and toxic lung damage in several studies. METHODS: We measured Ki67, Mcl-1, p53, CD79, and NOS-3 protein levels in the 1st, 7th, and 14th passages of bronchoepithelial human embryonic cell cultures. Gene expression of NKX2-1, SCGB1A1, SCGB3A2, FOXA1, FOXA2, MUC4, MUC5AC, and SFTPA1 was measured by real-time polymerase chain reaction. Using the methods of spectrophotometry, viscometry, and circular dichroism, we studied the ADEL-DNA interaction in vitro. RESULTS: Peptide ADEL regulates the levels of Ki67, Mcl-1, p53, CD79, and NOS-3 proteins in cell cultures of human bronchial epithelium in various passages. The strongest activating effect of peptide ADEL on bronchial epithelial cell proliferation through Ki67 and Mcl-1 was observed in "old" cell cultures. ADEL regulates the expression of genes involved in bronchial epithelium differentiation: NKX2-1, SCGB1A1, SCGB3A2, FOXA1, and FOXA2. ADEL also activates several genes, which reduced expression correlated with pathological lung development: MUC4, MUC5AC, and SFTPA1. Spectrophotometry, viscometry, and circular dichroism showed ADEL-DNA interaction, with a binding region in the major groove (N7 guanine). CONCLUSIONS: ADEL can bind to specific DNA regions and regulate gene expression and synthesis of proteins involved in the differentiation and maintenance of functional activity of the bronchial epithelium. Through activation of some specific gene expression, peptide ADEL may protect the bronchial epithelium from pulmonary pathology. ADEL also may have a geroprotective effect on bronchial tissue.

Modulation of action of wheat seedling endonucleases WEN1 and WEN2 by histones.

Wheat core histones and various subfractions of histone H1 modulate differently the action of endonucleases WEN1 and WEN2 from wheat seedlings. The character of this modulation depends on the nature of the histone and the methylation status of the substrate DNA. The modulation of enzyme action occurs at different stages of processive DNA hydrolysis and is accompanied by changes in the site specificity of the enzyme action. It seems that endonuclease WEN1 prefers to bind with protein-free DNA stretches in histone H1-DNA complex. The endonuclease WEN1 does not compete with histone H1/6 for DNA binding sites, but it does compete with histone H1/1, probably for binding with methylated sites of DNA. Unlike histone H1, the core histone H2b binds with endonuclease WEN1 and significantly increases its action. This is associated with changes in the site specificity of the enzyme action that is manifested by a significant increase in the amount of low molecular weight oligonucleotides and mononucleotides produced as a result of hydrolysis of DNA fragments with 120-140-bp length. The WEN2 endonuclease binds with histone-DNA complexes only through histones. The action of WEN2 is increased or decreased depending on the nature of the histone. Histone H1/1 stimulated the exonuclease activity of WEN2. It is supposed that endonucleases WEN1 and WEN2, in addition to the catalytic domain, should have a regulatory domain that is involved in binding of histones. As histone H1 is mainly located in the linker chromatin areas, it is suggested that WEN2 should attack DNA just in the chromatin linker zones. As differentiated from WEN2, DNA hydrolysis with endonuclease WEN1 is increased in the presence of core histones and, in particular, of H2b. Endonuclease WEN1 initially attacks different DNA sites in chromatin than WEN2. Endonuclease WEN2 activity can be increased or diminished depending on presence of histone H1 subfractions. It seems that just different fractions of the histone H1 are responsible for regulation of the stepwise DNA degradation by endonuclease WEN2 during apoptosis. Modulation of the action of the endonucleases by histones can play a significant role in the epigenetic regulation of various genetic processes and functional activity of genes.

Interaction of short peptides with FITC-labeled wheat histones and their complexes with deoxyribooligonucleotides.

Judging from fluorescence modulation (quenching), short peptides (Ala-Glu-Asp-Gly, Glu-Asp-Arg, Ala-Glu-Asp-Leu, Lys-Glu-Asp-Gly, Ala-Glu-Asp-Arg, and Lys-Glu-Asp-Trp) bind with FITC-labeled wheat histones H1, H2B, H3, and H4. This results from the interaction of the peptides with the N-terminal histone regions that contain respective and seemingly homologous peptide-binding motifs. Because homologous amino acid sequences in wheat core histones were not found, the peptides seem to bind with some core histone regions having specific conformational structure. Peptide binding with histones and histone-deoxyribooligonucleotide complexes depends on the nature of the histone and the primary structures of the peptides and oligonucleotides; thus, it is site specific. Histones H1 bind preferentially with single-stranded oligonucleotides by homologous sites in the C-terminal region of the protein. Unlike histone H1, the core histones bind predominantly with double-stranded methylated oligonucleotides and methylated DNA. Stern-Volmer constants of interaction of histone H1 and core histones with double-stranded hemimethylated oligonucleotides are higher compared with that of binding with unmethylated ones. DNA or deoxyribooligonucleotides in a complex with histones can enhance or inhibit peptide binding. It is suggested that site-specific interactions of short biologically active peptides with histone tails can serve in chromatin as control epigenetic mechanisms of regulation of gene activity and cellular differentiation.

Mechanisms of catalytic action and chemical modifications of endonucleases WEN1 and WEN2 from wheat seedlings.

Hydrolysis of DNA catalyzed by wheat endonucleases WEN1 and WEN2 is pronouncedly processive. A correlation has been revealed between appearance of new products of DNA hydrolysis with different length and conformational changes in the enzymes. The first conformational conversion of the endonucleases is associated with appearance of large fragments of DNA hydrolysis with length longer than 500 bp, and the second conversion is associated with formation of oligonucleotides with length of 120-140 bp, and the third conversion is associated with formation of short oligonucleotides and mononucleotides. Formation of the DNA-enzyme complex is accompanied by appearance of fluorescence at λ = 410-440 nm. The intensity, positions, and numbers of maximums of the fluorescence spectra of DNA-WEN1 and DNA-WEN2 complexes are different and depend on the methylation status of the DNA and on the presence of Mg2+. The endonucleases hydrolyze DNA by two mechanisms: one is metal-independent, and the other depends on one or two Mg2+ ions. One Mg2+ ion is located inside the catalytic center of WEN1, whereas the WEN2 center contains two Mg2+ ions. The first (site-specific) stage of DNA hydrolysis does not depend on Mg2+. Mg2+ ions evoke changes in the site specificity of the endonuclease action (WEN1) and abolish their ability to recognize the methylation status of DNA. Products of DNA hydrolysis by endonucleases WEN1 and WEN2 in the presence of Mg2+ are similar in length (120-140 bp). The endonucleases have at least two centers (domains) - catalytic and substrate-binding. Two histidine and apparently two lysine plus two dicarboxylic amino acid residues are present inside the catalytic center of WEN1. The catalytic center of WEN2 contains at least one histidine residue and apparently two residues of aspartic or glutamic acid, which are involved in coordination of the metal ions. The catalytic centers of WEN1 and WEN2 seem to be formed, respectively, by HD/E(D/EK)KH and HD/ED/E amino acid residues. The site-specificity of the endonuclease action is due to the DNA-binding domain. This domain contains dicarboxylic amino acid residues, which seem to be responsible for sensitivity of the enzymes to the methylation status of DNA. The hydroxyl groups of tyrosine residues in the enzymes also seem to contribute to recognizing methylated bases in DNA.

Role of peptides in epigenetic regulation of gene activities in ontogeny.

The authors develop a new concept most fully reflecting the evolutional and biological role of peptides in the organism. Wide spectrum of peptide effects realized through regulation of the expression of certain genes is aimed at the maintenance of homeostasis, inhibition of the genetic aging program realization, and lifespan prolongation.

Processing character of the action of wheat endonucleases WEN1 and WEN2. Kinetic parameters.

The wheat seedling endonucleases WEN1 and WEN2 dependent on Mg(2+), Ca(2+), and S-adenosyl-L-methionine (SAM) and sensitive to the substrate DNA methylation status have an expressed processing action. The enzymes hydrolyze DNA at a few subsequent stages: first, they split λ phage DNA specifically at CNG-sites (WEN1) with liberation of large fragments; second, they hydrolyze these fragments to 120-140 bp oligonucleotides that finally are hydrolyzed to very short fragments and mononucleotides. Initial stages of DNA hydrolysis may proceed in the absence of Mg(2+), but subsequent hydrolysis stages are very strongly stimulated by Mg(2+). It cannot be ruled out that modulation of enzymatic activity with Mg(2+) and probably with DNA fragments formed is associated with reorganization of the structure of eukaryotic (wheat) endonucleases with respective changes in their catalytic properties and site specificity of action. Michaelis constant value for WEN1 endonuclease on hydrolysis of methylated λ phage DNA containing Cm(5)CWGG and Gm(6)ATC sites is four-fold lower compared with that observed on hydrolysis of unmethylated λ phage DNA. This may indicate that affinity of WEN1 enzyme to methylated DNA is higher than that to unmethylated DNA. In the presence of SAM, the Michaelis constant for WEN2 on the DNA hydrolysis stage characterized by formation of 120-140 bp fragments is decreased, but for WEN1 it is increased by 1.5-2.0-fold. This means that SAM inhibits WEN1 but stimulates WEN2. Thus, wheat endonucleases WEN1 and WEN2 differ significantly in affinities to substrate DNAs with different methylation status, in velocities of DNA hydrolysis, and time of production of DNA fragments of similar length. It seems that the investigated plant endonucleases can hydrolyze DNA in the nucleus as well to both large and very short fragments including mononucleotides, that is, in particular, essential for utilization of cell nucleic acid material during apoptosis.

Endonucleases and apoptosis in animals.

Endonucleases are the main instruments of obligatory DNA degradation in apoptosis. Many endonucleases have marked processive action; initially they split DNA in chromatin into very large domains, and then they perform in it internucleosomal fragmentation of DNA followed by its hydrolysis to small fragments (oligonucleotides). During apoptosis, DNA of chromatin is attacked by many nucleases that are different in activity, specificity, and order of action. The activity of every endonuclease is regulated in the cell through its own regulatory mechanism (metal ions and other effectors, possibly also S-adenosylmethionine). Apoptosis is impossible without endonucleases as far as it leads to accumulation of unnecessary (defective) DNA, disorders in cell differentiation, embryogenesis, the organism's development, and is accompanied by various severe diseases. The interpretation of the structure and functions of endonucleases and of the nature and action of their modulating effectors is important not only for elucidation of mechanisms of apoptosis, but also for regulation and control of programmed cell death, cell differentiation, and development of organisms.

Penetration of short fluorescence-labeled peptides into the nucleus in HeLa cells and in vitro specific interaction of the peptides with deoxyribooligonucleotides and DNA.

Marked fluorescence in cytoplasm, nucleus, and nucleolus was observed in HeLa cells after incubation with each of several fluorescein isothiocyanate-labeled peptides (epithalon, Ala-Glu-Asp-Gly; pinealon, Glu-Asp-Arg; testagen, Lys-Glu-Asp-Gly). This means that short biologically active peptides are able to penetrate into an animal cell and its nucleus and, in principle they may interact with various components of cytoplasm and nucleus including DNA and RNA. It was established that various initial (intact) peptides differently affect the fluorescence of the 5,6-carboxyfluorescein-labeled deoxyribooligonucleotides and DNA-ethidium bromide complexes. The Stern-Volmer constants characterizing the degree of fluorescence quenching of various single- and double-stranded fluorescence-labeled deoxyribooligonucleotides with short peptides used were different depending on the peptide primary structures. This indicates the specific interaction between short biologically active peptides and nucleic acid structures. On binding to them, the peptides discriminate between different nucleotide sequences and recognize even their cytosine methylation status. Judging from corresponding constants of the fluorescence quenching, the epithalon, pinealon, and bronchogen (Ala-Glu-Asp-Leu) bind preferentially with deoxyribooligonucleotides containing CNG sequence (CNG sites are targets for cytosine DNA methylation in eukaryotes). Epithalon, testagen, and pinealon seem to preferentially bind with CAG- but bronchogen with CTG-containing sequences. The site-specific interactions of peptides with DNA can control epigenetically the cell genetic functions, and they seem to play an important role in regulation of gene activity even at the earliest stages of life origin and in evolution.

CNG site-specific and methyl-sensitive endonuclease WEN1 from wheat seedlings.

Endonuclease WEN1 with apparent molecular mass about 27 kDa isolated from cytoplasmic vesicular fraction of aging coleoptiles of wheat seedlings has expressed site specificity action. This is a first detection and isolation of a site-specific endonuclease from higher eukaryotes, in general, and higher plants, in particular. The enzyme hydrolyzes deoxyribooligonucleotides of different composition on CNG (N is G, A, C, or T) sites by splitting the phosphodiester bond between C and N nucleotide residues in CNG sequence independent from neighbor nucleotide context except for CCCG. WEN1 prefers to hydrolyze methylated λ phage DNA and double-stranded deoxyribooligonucleotides containing 5-methylcytosine sites (m(5)CAG, m(5)CTG) compared with unmethylated substrates. The enzyme is also able to hydrolyze single-stranded substrates, but in this case it splits unmethylated substrates predominantly. Detection in wheat seedlings of WEN1 endonuclease that is site specific, sensitive to the substrate methylation status, and modulated with S-adenosyl-L-methionine indicates that in higher plants restriction--modification systems or some of their elements, at least, may exist.

Site-specific binding of short peptides with DNA modulated eukaryotic endonuclease activity.

Short peptides (2-4 amino acid residues) inhibit or stimulate hydrolysis of λ phage DNA by eukaryotic endonucleases WEN1 and WEN2 depending on DNA methylation status. Peptide modulation of endonucleases activity most likely appears as a result of their binding to DNA. Peptides discriminate (recognize) not only certain DNA sequences, but also their methylation status. Apart from intact DNA, the test peptides bind to single-stranded DNA structures (oligonucleotides) containing NG- and CG-sites methylated in eukaryotes. Peptides affect the set of hydrolyzed sites during endonuclease hydrolysis of double-stranded structures. The effects of peptides with different primary structure on DNA hydrolysis by endonucleases are different and are modulated by histones (histone H1). Site-specific peptide interactions with DNA may epigenetically control genetic functions of the cell. These interactions probably played an important role at the very early stages of evolution.

H1 histone modulates DNA hydrolysis with WEN1 and WEN2 endonucleases from wheat coleoptiles.

We show that total H1 histone from wheat seedlings or rat liver enhances hydrolysis of lambda phage DNA with plant endonucleases WEN1 and WEN2 isolated from wheat coleoptiles. Optimal DNA/protein weight ratio in the hydrolysis reaction is 1 : 1. The action of fractions I and IV (obtained from total wheat H1 histone by electrophoresis) on DNA hydrolysis with WEN1 and WEN2 enzymes depends on the DNA methylation status. Fraction IV of wheat histone H1 stimulates hydrolysis of unmethylated lambda phage DNA with WEN1 and WEN2 enzymes. Hydrolysis of methylated lambda phage DNA (it contains 5-methylcytosine in Cm(5)CWGG sequences and N(6)-methyladenine in Gm(6)ATC sites) with WEN1 is inhibited with fractions I and IV of wheat H1 histone. Fractions II and III of wheat H1 histone do not influence DNA hydrolysis with WEN1 and WEN2. S-Adenosyl-L-methionine (SAM) stimulates activity of these plant enzymes. But in the presence of H1 histone, SAM does not add to the ability of the enzyme to hydrolyze more DNA compared with that induced with H1 histone itself. Therefore, the stimulating effects of SAM and H1 histone on DNA hydrolysis with plant endonucleases may be similar. It could be suggested that SAM and H1 histone can induce more or less analogous allosteric transformations in the structure of the investigated plant endonucleases. Thus, DNA hydrolysis with plant endonucleases is modulated with total H1 histone. H1 histone fractions affect DNA hydrolysis in a different fashion; they enhance or inhibit hydrolysis depending on the DNA methylation status. We suggest that H1 histone changes site specificity of endonucleases or it might be responsible for formation of new or masking of old sites available for these enzymes due to changes in DNA structure induced in a DNA-histone complex.