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Z Avramova

Publications and source records attributed to Z Avramova.

28 records · Page 2Linked to original sources
PubMed1987

Stable DNA-protein complexes in eukaryotic chromatin.

Demembranized sperm and somatic nuclei of mammalian origin were extracted with high salt/urea/2-mercaptoethanol, treated with detergents and purified in CsCl density gradients to isolate DNA. Under these conditions a protein component still remained bound to DNA. This stable DNA-protein complex could be reduced to an oligodeoxynucleotide-peptide complex by extensive sequential digestions with DNase I and Pronase E. Chemical and enzymatic treatments of this complex indicated the presence of a phosphoester bond between DNA and a hydroxyamino acid. Two-dimensional tryptic peptide mapping revealed a remarkable similarity among the covalently linked protein components in all types of chromatin studied. These maps differed from the maps of mammalian topoisomerases I and II.

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PubMed1987

A study on the heterogeneity of histone H1 from dry maize embryos.

Maize dry embryo cells have been chosen as model for the study of H1 histone complement of metabolically inactive plant chromatin. H1 has been fractionated into two distinct bands in acetic acid/urea gels. Analysis of each of these bands in SDS-containing gels has shown that maize embryo H1 is heterogeneous, consisting of at least six proteins. Cross-reactivity of maize H1 species with antibodies against mouse liver total H1 and against its individual variants indicates that they share common immunological determinants but differ substantially from each other when compared by peptide mapping. It is concluded that a couple of the plant H1 subfractions are related to animal H1A histone and that another one is related to H1B histone. The other three maize H1 variants are closely related to each other and they also share common immunological determinants with mouse H1A, and possibly with H1B. All maize H1 species slightly cross-react with antibodies against H1 degree, suggesting that no one of the plant subfractions could be characterized as H1 degree in particular. One of the proteins co-extracted and comigrating with H1 is most probably an embryo storage protein.

Animals↗
PubMed1987

Tightly bound nonprotamine proteins from ram sperm nuclei studied by one- and two-dimensional peptide mapping.

The tightly bound proteins of ram sperm nuclei (TBSP) have been recovered as a fraction co-sedimenting with DNA after high salt-urea deprotamination of the nuclei. TBSP were studied by two-dimensional (2D)-tryptic peptide mapping and by one-dimensional (1D)-partial proteolysis mapping. The 2D maps revealed a strong homology among the proteins, irrespective of substantial differences in their molecular masses. This homology was supported also by the 1D-mapping data. The 2D-tryptic maps of TBSP were compared to those of lamb liver lamins but no apparent similarity was detected. TBSP were found to react positively to a test for the presence of carbohydrate residues, suggesting that these proteins are glycoproteins as established earlier for the lamins. The 2D maps of several proteins of seminal plasma origin, used as a control, displayed completely different peptide profiles.

Animals↗
PubMed1985

An H1-like protein from the sperm chromatin of Mytilus galloprovincialis.

We have isolated and purified a sperm-specific protein (S3) from the mussel M. galloprovincialis. Antibodies against S3 were raised in rabbits and used for its immunological comparison to somatic histones. The results showed that S3 did not share common immunological determinants with H2b or any other core histone-contrary to the suggestion that it was an H2b-like protein (Ausio and Subirana, 1982). With H1 there was a crossreaction between S3 and anti-H1 as well as with H1 and anti-S3. Although similar to somatic H1, S3 is not identical with it. This fact makes S3 an interesting example of another protein of the H1-H5 type, present in a completely inactive chromatin.

Animals↗
PubMed1984

Biochemical and ultrastructural study of the sperm chromatin from Mytilus galloprovincialis.

Protein composition and ultrastructure of the mature spermatozoa of the mussel Mytilus galloprovincialis were studied upon gradual decondensation of the nuclei with increasing NaCl concentration. Three types of protein were found, associated with the sperm DNA: (1) the sperm-specific proteins S1, S2 and S3 (80% of the acid-soluble proteins); (2) the four core histones (20%); (3) three non-histone proteins tightly bound to DNA (about 4 micrograms protein per 100 micrograms DNA). The sperm-specific protein S3 was the first to dissociate at about 0.5 M NaCl and electron micrographs of spread nuclei indicated its participation in the final compaction of the nucleus. Hypotonically treated sperm nuclei revealed the presence of 21-25 nm large granules irregularly scattered along some of the DNA fibers. These granules correspond to the 'superbeads' of histone-containing chromatins. The tightly bound non-histone proteins were represented by a triplet in the range 60-80 kD. They formed 30-60 nm large annular bodies holding DNA fibers and resisting high salt-detergent treatment.

Animals↗
PubMed1983

Trout sperm chromatin. I. Biochemical and immunological study of the protein composition.

Compact sperm chromatin was obtained from mature trout sperm nuclei resistant to sonication and detergent treatments. 0.5 to 2 M NaCl caused a gradual decondensation of this chromatin and the dependence of the percentage of dissociated proteins on the salt concentration indicated cooperativity of the dissociation process. Urea alone was insufficient to decondense the nuclei. The only proteins dissociated from the sperm nuclei by NaCl alone or combined with urea were protamines. Besides protamines, tightly bound nonprotamine proteins resisting high salt-urea extraction were detected in the sperm nucleus. Part of them could be solubilized by 1% sodium dodecyl sulphate (SDS) and displayed the characteristics of the core histones: they were soluble in 0.25 N H2SO4, their electrophoretic mobilities were similar to those of trout liver core histones, and they shared common antigenic determinants with the latter. The rest of the tightly bound proteins resisted 1% SDS treatment and could be obtained after an extensive digestion of DNA with DNase I. These were nonhistone proteins similar in mobility to the protein triplet characteristic of the lamina-pore complex and an additional high molecular weight protein.

Animals↗
PubMed1983

Trout sperm chromatin. II. Ultrastructural aspects after salt dissociation of proteins.

The ultrastructural organization of the trout sperm nucleus was studied in ultrathin sections and spread preparations after partial decondensation of the nucleus with increasing NaCl concentrations. The obtained results suggest that the organization of the trout sperm chromatin is much more complex than a pure nucleoprotamine. Three types of complexes were observed. The first one results from the association of DNA with protamines. This complex appears as a fibrous network when partially decondensed nuclei are digested with DNase I indicating that at least a part of DNA remains protected by protamines and favours models accepting a colinear alignment of the latter on the DNA molecules. The second type of structures represent the DNA-protamine fibers compacted into dense clumps which appear as separate compaction units seen upon partial decondensation of the sperm nucleus. A third type are complexes of the ring-shaped granular bodies tightly associated with DNA and resisting high salt-urea and detergent treatment.

Animals↗
PubMed1981

Nonprotamine nucleoprotein ultrastructures in mature ram sperm nuclei.

Nuclei from mature ram spermatozoa were treated with a solution of 0.25 M 2-mercaptoethanol, 2 M NaCl, 4 to 8 M urea to dissociate protamines and some other proteins from DNA. The material remaining after such a treatment was spread for electron microscopy in the microcentrifugation chamber. Two types of structures were observed determined by proteins of nonprotamine nature. The first type was represented by protein bodies of an irregular ringlike shape to which DNA fibers were anchored to form a network. This structure determines the shape of the sperm head and may correspond to the nuclear skeleton described in somatic cells. The second type of structures were chromatin fibers containing beads of approximately nucleosomal size. These rough fibers were unevenly distributed in the nucleus and were much less frequent than the smooth fibers usually observed. Both types of structures were determined by unusually firmly bound proteins. They were resistant not only to the reduction of disulfide bonds and to high salt and urea concentrations but also to 2% sodium dodecysulfate and to 5 M guanidine chloride. These results show that apart from packing of DNA in a nucleoprotamine complex, two levels of DNA organization can be observed in the ram sperm nucleus: the first level consists of two kinds of DNA fibers (smooth and rough); in the second level of DNA is organized in domains fixed by a proteinous nuclear skeleton.

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