Functional histone antibody fragments traverse the nuclear envelope

Factors important in the translocation process of proteins across the nuclear membrane were studied by microinjecting either fluoresceinated nonimmune IgG and F(ab)2 or the corresponding molecules, prepared from antisera to histones, into the nucleus and cytoplasm of human fibroblasts. Intact IgG from both preparations remained at the site of injection regardless of whether it was injected into the nucleus or the cytoplasm. In contrast, nonimmune F(ab)2 distributed uniformly throughout the cell. The F(ab)2 derived from affinity-pure antihistone moves into the nucleus after cytoplasmic injection and remains in the nucleus after nuclear microinjection. The migration of the antihistone F(ab)2 into the nucleus results in inhibition of uridine incorporation in the nuclei of the microinjected cells. We conclude that non-nuclear proteins, devoid of specific signal sequences, traverse the nuclear membrane and accumulate in the nucleus provided their radius of gyration is less than 55A and the nucleus contains binding sites for these molecules. These findings support the model of "quasibifunctional binding sites" as a driving force for nuclear accumulation of proteins. The results also indicate that active F(ab)2 fragments, microinjected into somatic cells, can bind to their antigenic sites suggesting that microinjection of active antibody fragments can be used to study the location and function of nuclear components in living cells.

Specific binding of Alu sequences by HeLa nuclear extracts

Plasmid Blur 8 which contains the 300bp human Alu consensus sequence and plasmid pBR322 were digested with restriction enzymes and the fragments obtained end labelled with 32P-gamma-ATP. The end labelled fragments were incubated with HeLa nuclear extracts and the incubation mixtures passed through a nitrocellulose filter. The 300bp alu consensus sequence was preferentially retained on the filter. The HeLa nuclear extract did not preferentially bind any fragments generated from pBR322 and histones which bind nonspecifically all DNA fragments did not preferentially bind the alu sequence. We conclude that the HeLa nuclear extract contains components which specifically bind the human alu sequence.

Effect of X-radiation on DNA and histone synthesis in ataxia telangiectasia and normal lymphoblastoid cells

The possibility that the radiosensitivity of lymphoblastoid cell lines from patients with ataxia telangiectasia (A-T) is due to an aberrant content of histones has been examined. The histone pattern of lymphoblastoid cell lines derived from A-T patients was found to be indistinguishable from that obtained from normal individuals. X-ray irradiation led to a greater decrease in cell growth rate in the A-T cells than in the normal cells but was accompanied by a greater decrease of DNA synthesis rate in the normal cells. This difference in radiosensitivity was not reflected in differences in the content or rates of synthesis of histones or of major non-histone proteins in these cells. Reduction in the rate of DNA synthesis was not associated with the appearance of the lysine-rich histone variant H1. We conclude that the hypersensitivity to ionizing radiation in A-T cells is not due to fundamental differences in the composition or synthesis of the major chromosomal proteins.

Inhibition of transcription in somatic cells by microinjection of antibodies to chromosomal proteins

The in vivo function of defined chromosomal proteins was examined by microinjecting purified antibody and antibody fragments into living fibroblasts. The involvement of histones and chromosomal high mobility group proteins HMG-1, 2, and 17 in transcription was visualized by studying the [3H]uridine incorporation in KD human fibroblasts after microinjection of fluoresceinated antibodies to these proteins. Nuclear uridine incorporation was not affected by microinjection of control antibodies or by the presence of immune complexes formed after microinjection of antibodies to chromosomal proteins that are not involved in transcription. In contrast, injection of anti-histone IgG, F(ab')2, or Fab and anti-HMG-17 IgG causes a significant reduction in transcription. The reduction is proportional to the amount of antibody introduced into the cell. We conclude that histones and protein HMG-17 are present on transcribed regions of the genome and that passage of RNA polymerase along the chromatin fiber is prevented by antibody binding to these proteins.

High mobility group proteins of amphibian oocytes: a large storage pool of a soluble high mobility group-1-like protein and involvement in transcriptional events

Oocytes of several amphibian species (Xenopus laevis, Rana temporaria, and Pleurodeles waltlii) contained a relatively large pool of nonchromatin-bound, soluble high mobility group (HMG) protein with properties similar to those of calf thymus proteins HMG-1 and HMG-2 (protein HMG-A; A, amphibian). About half of this soluble HMG-A was located in the nuclear sap, the other half was recovered in enucleated ooplasms. This protein was identified by its mobility on one- and two-dimensional gel electrophoresis, by binding of antibodies to calf thymus HMG-1 to polypeptides electrophoretically separated and blotted on nitrocellulose paper, and by tryptic peptide mapping of radioiodinated polypeptides. Most, if not all, of the HMG-A in the soluble nuclear protein fraction, preparatively defined as supernatant obtained after centrifugation at 100,000 g for 1 h, was in free monomeric form, apparently not bound to other proteins. On gel filtration it eluted with a mean peak corresponding to an apparent molecular weight of approximately 25,000; on sucrose gradient centrifugation it appeared with a very low S value (2-3 S), and on isoelectric focusing it appeared in fractions ranging from pH approximately 7 to 9. This soluble HMG-A was retained on DEAE-Sephacel but could be eluted already at moderate salt concentrations (0.2 M KCl). In oocytes of various stages of oogenesis HMG-A was accumulated in the nucleus up to concentrations of approximately 14 ng per nucleus (in Xenopus), corresponding to approximately 0.2 mg/ml, similar to those of the nucleosomal core histones. This nuclear concentration is also demonstrated using immunofluorescence microscopy. When antibodies to bovine HMG-1 were microinjected into nuclei of living oocytes of Pleurodeles the lateral loops of the lampbrush chromosomes gradually retracted and the whole chromosomes condensed. As shown using electron microscopy of spread chromatin from such injected oocyte nuclei, this process of loop retraction was accompanied by the appearance of variously-sized and irregularly-spaced gaps within transcriptional units of chromosomal loops but not of nucleoli, indicating that the transcription of non-nucleolar genes was specifically inhibited by this treatment and hence involved an HMG-1-like protein. These data show that proteins of the HMG-1 and -2 category, which are usually chromatin-bound components, can exist, at least in amphibian oocytes, in a free soluble monomeric form, apparently not bound to other molecules. The possible role of this large oocyte pool of soluble HMG-A in early embryogenesis is discussed as well as the possible existence of soluble HMG proteins in other cells.

The binding of a carcinogen to the nucleosomal and non-nucleosomal regions of the simian virus 40 chromosome in vivo

The effect of chromatin structure on the binding of a chemical carcinogen to the genomic DNA was studied. The binding in vivo of the ultimate carcinogen, benzo-pyrene 7,8,-diol,-9,10-epoxide, to various regions of the SV40 chromosome was revealed by an immunological method. Particular attention was given to restriction fragments which include the origin of replication which is "non-nucleosomal" in a significant fraction of the chromosomes. The distribution of (+/-) trans-7,8-dihydrobenzo[alpha]pyrene-7,8-diol-9,10-epoxide (BPDE) adducts was studied in 1) SV40 DNA modified in vitro to a level of 20 adducts/molecule, 2) DNA from SV40 chromosomes modified in vivo to a level of less than 1 adduct, and 3) DNA from only those chromosomes with an open origin of replication. In other experiments, the binding of BPDE to the origin region was compared to the binding to nucleosome core particle DNA from the viral chromosome. The origin region bound 1.7-fold more BPDE than core DNA, while linker DNA is 3-fold more modified than core DNA. However, the origin region was only about 20% more modified than any other region of the chromosome. We conclude that while the conformation of the DNA in chromatin has a slight effect on its accessibility to the carcinogen, the SV40 chromosome does not contain a particular "hot spot" which is preferentially modified by BPDE.

Immunological detection of carcinogen-modified DNA fragments after in vivo modification of cellular and viral chromatin

Antibodies specific for DNA modified by (+/-)-trans-7, 8-dihydrobenzo(a)pyrene-7,8-diol-9, 10-epoxide have been used to quantitate the relative modification level in fragments derived from pBR322 DNA from cellular DNA and in the coding and noncoding strands of simian virus 40 DNA. DNA fragments with a covalent molar modification level ranging from less than 1 to over 200 are resolved by agarose gel electrophoresis and transferred to diazobenzyloxymethyl cellulose paper. The paper is incubated with antibodies specific to carcinogen-modified DNA, and the location of the antibody is visualized by autoradiography after incubation with 125I-protein A. The binding of antibodies is directly proportional to the level of DNA modification. Using this technique, we find that linker DNA is about 2.5- to 3-fold more accessible to (+/-)-trans-7,8-dehydrobenzo(a)pyrene-7, 8-diol-9, 10-epoxide than nucleosomal core DNA and that under in vivo conditions the coding and noncoding strands of the simian virus 40 chromosome are equally accessible to trans-7,8-dihydrobenzo[a]pyrene-7,8-diol-9, 10-epoxide. The approach described allows assessment of the relative level of modification in any DNA sequence which can be subjected to gel electrophoresis.

Selective exposure of antigenic determinants in chromosomal proteins upon gene activation in polytene chromosomes

The immunological accessibility of the nucleosomal core protein H3 and non-histone protein, HMG-1, was studied in transcriptionally active regions of Chironomus thummi polytene chromosomes. Chromosomal loci were decondensed by incubating isolated salivary glands in various salt solutions or hemolymph. Indirect immunofluorescence studies on these chromosomes using anti-sera to histone H3 revealed that the puffed regions were depleted of fluorescence. The lack of fluorescence could be correlated with the degree of puffing and the level of transcriptional activity. The puffed regions fluoresce after anti-H3 addition if the chromosomes are not cross-linked with formaldehyde, and if prior to the addition of antibodies the chromosomes are treated with 45% acetic acid. We conclude that, whereas histone H3 is present in the puffed regions, its antigenic determinants are sterically hindered by components which are extractable by 45% acetic acid. On the other hand, the antigenic determinants of protein HMG-1 are always available to antibody binding in puffed regions, as well as other chromosomal areas.

Immunological evidence for the in vivo occurrence of a crosslinked complex of poly(ADP-ribosylated) histone H1

The poly(ADP-ribosylation) of histones, which occurs within a limited and functionally specific domain of chromatin, is a novel post-translational modification. However, in the past it has been difficult to study this process in living cells because the substrate of the reaction (NAD) does not permeate the plasma membrane. In the current study, antibodies specific for histone H1 and poly(ADP-ribose) were used to study the occurrence of poly(ADP-ribose)+ species of H1 in vivo. Perchloric acid-extracted proteins from synchronously growing HeLa cells were fractionated by electrophoresis and transferred to nitrocellulose, and the transferred moieties were allowed to react with the specific antibodies and then with 125I-labeled protein A. The results conclusively demonstrate the natural occurrence of poly(ADP-ribose)-crosslinked complexes of histone H1 (i.e., H1 dimer), at the S/G2 phase transition of the cell cycle.

Antigenic determinants of high mobility group chromosomal proteins 1 and 2

The antigenic determinants of nonhistone high mobility group chromosomal proteins 1 (HMG-1) and 2 (HMG-2) were studied with rabbit antisera elicited against HMG-1 and against HMG-2 and monoclonal antibodies elicited by HMG-1. The monoclonal antibodies did not distinguish between the two proteins, suggesting that they have specificity toward a shared determinant. Whereas anti-HMG-1 did not, anti-HMG-2 did distinguish between the proteins, suggesting that the anti-HMG-2 serum contains antibodies against peptides which differ between the proteins. Peptides were generated from HMG-1 and HMG-2 by controlled digestion with trypsin and pepsin. Analysis of the digests by ELISA and by sodium dodecyl sulfate electrophoresis followed by diazobenzyloxymethyl transfer, antibody binding and autoradiography revealed that most of the antibodies are against sequential determinants some of which are smaller than 3000 in molecular weight.

Antibodies against the folding domain of histone H5 cross-react with H1(0) but not with H1

Antibodies to the folding domain (residues 22-100) of histone H5 were elicited in rabbits. Analysis of the specificity of these antibodies by enzyme-linked immunoassay and by diazobenzyloxymethyl cellulose transfer techniques revealed that the antibody cross-reacts strongly with intact H5 and histones H1(0)a and H1(0)b purified from ox liver but not with the four core calf thymus, or with high mobility group proteins. We conclude that the globular region of H5 is serologically homologous to that of H1 degrees and suggest that possible functional similarities between the two proteins reside in this region.

Antibody to poly(adenosine diphosphate-ribose) polymerase and its use in chromatin analysis

To facilitate investigations on the organization of poly (ADP-Rib) polymerase in chromatin, and to elucidate its biological function, polymerase purified from HeLa nuclei was used to elicit antibodies in mice. The anti-polymerase sera was found to be specific by multiple criteria. The association of polymerase with oligonucleosomes of differing chain size was determined by the specific binding of polymerase antibody (and as control, anti-histone H3) to nitrocellulose transfers of native electrophoretic gels of these particles. By this technique, polymerase appears to be associated with a select subclass of nucleosomes. Further resolution of the polymerase binding sites within nucleosome classes was achieved with the antibody by two-dimensional native polyacrylamide gel electrophoresis and nitrocellulose transfer.

Autoantibodies to nucleosomal proteins: antibodies to HMG-17 in autoimmune diseases

The relative amounts of autoantibodies against defined nucleosomal proteins present in serums from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and mixed connective tissue disease (MCTD) have been examined by an enzyme-linked immunoassay. Autoantibodies to nucleosomal proteins were detected in 45 percent of the patients with SLE, 18 percent of the MCTD patients, and none of the RA patients. The results suggest that, in SLE, antibodies are formed against a subset of nucleosomes which contain protein HMG-17.

Immunochemical visualization of binding of the chemical carcinogen benzo(a)pyrene diol-epoxide 1 to the genome

antisera against DNA modified with r-7,t-8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE-1) was elicited in rabbits. Such sera reached with either single- or double-stranded modified DNA but not with unmodified DNA, free benzo(a)pyrene, or proteins modified by BPDE-1. Indirect immunofluorescence studies indicated that the immunoglobulin G in the sera bound specifically to the nuclei of KD cells which were treated with BPDE-1. The intensity of fluorescence was proportional to the dose of BPDE-1 used to treat the cells. About 50% of the BPDE-1-DNA adducts remained bound to DNA 24 hr after the removal of the carcinogen. The location of BPDE-1-modified bases in Col E1 DNA was visualized by immunoelectron microscopy.

Localization of chromosomal protein HMG-1 in polytene chromosomes of Chironomus thummi

The distribution of accessible antigenic sites in the chromosomal protein high mobility group one (HMG-1) in Chironomus thummi polytene chromosomes is visualized by immunofluorescence. The results indicate that (a) HMG-1 is distributed in a distinct banding pattern along the entire length of the chromosomes; (b) the banding pattern obtained with fluorescent antibody does not strictly correspond to that observed by phase-contrast microscopy; and (c) the amount of HMG-1 increases, and the fluorescent banding pattern changes, during the development of the organism. Our findings suggest that the protein may be involved in the modulation of the structure of selected loci in the chromosome.

Immunochemical detection of chromosomal protein HMG-17 in chromatin subunits

Chromosomal protein HMG-17, purified from calf thymus, has been used to elicit specific antibodies in rabbits. Specific serological reaction between the antigen and the antisera is demonstrated by solid-phase radioimmunoassay and by competitive inhibition assays. The antisera did not cross-react with histones or other chromosomal HMG proteins. The antisera bound specifically to chromatin subunits isolated from HeLa cells, demonstrating that it may be used to study the in situ organization of this chromosomal protein. Chromatin purified from HeLa nuclei was digested with micrococcal nuclease, and the resulting mono- and oligonucleosomes were fractionated on a sucrose gradient. Analyses of the content of chromosomal proteins HMG-1, HMG-17, and H4 in different size nucleosomal particles, by the solid-phase radioimmunoassay, reveal that the distribution of HMG-17 was the same as that of H4, but different from that of HMG-1.

Chromatin subunits elicit species-specific antibodies against nucleoprotein antigenic determinants

Nucleosomes composed of 195 base pairs of DNA associated with histones H2A, H2B, H3, and H4 purified from chicken erythrocyte nuclei were used to elicit antibodies in rabbits. Specific serological reaction between the antisera and the nucleosomes is demonstrated by immunodiffusion, immunofluorescence, microcomplement fixation, solid-phase radioimmunoassay, immunosedimentation, and polyacrylamide gel electrophoresis of 5'-32P end-labeled nucleosomes. The antisera did not react with DNA extracted from these nucleosomes, core histones, or the cross-linked histone octamer from chicken erythocytes, calf thymus total histones, or chromosomal proteins HMG-1 or HMG-17. Nucleosome antigenicity was not affected by redigestion with micrococcal nuclease. Digestion with DNase I brought about 50% loss of reactivity while digestion with trypsin or proteinase K resulted in total loss of activity. The antisera reacted strongly with trimer, dimer, and monomer nucleosomes as well as with the core particle (145 base pairs of DNA) and subnucleosome (greater than 145 base pairs) obtained from chicken. It reacted less well with nucleosomes obtained from HeLa cells and was almost totally devoid of activity against chromatin particles obtained from rat liver or wheat germ. Experiments employing the technique of transferring proteins from a polyacrylamide gel to diazobenzyloxymethyl paper and visualization of antigens by autoradiography excluded the possibility that the serum contains antibodies against tissue-specific antigens which are found in small amounts but are very immunogenic. It is concluded that most of the anitbodies in the sera are directed against nucleoprotein antigenic determinants composed of the N-terminal portion of the histones and segments of DNA. Antibody binding is dependent on contact between the histone and DNA segments and is independent of the integrity of the entire nucleosome. Thus, certain histone DNA contacts remain intact even though the structure of the nucleosome has been disrupted.

High mobility group chromosomal proteins isolated from muclei and cytosol of cultured hepatoma cells are similar

Using sequential chromatography on columns containing immobilized double-stranded DNA and single-stranded DNA, we have purified a protein from the cytosol of an established line of cultured rat hepatoma cells that, by several criteria, is a high mobility group (HMG) protein. Analyses of DNA binding properties, electrophoretic mobilities, amino acid compositions, and immunochemical reactivities reveal that the cytosolic protein is the same protein as HMG-1 isolated from the purified chromatin of the same cell line. Thus, authentic HMG-1 appears to be at least partially responsible for the cytoplasmic fluorescence observed when mammalian cells are stained with fluorescece observed when mammalian cells are stained with fluorescent-labeled, affinity-purified antibodies against HMG-1 [Bustin, M., & Neihart, N.K. (1979) Cell 16, 181-189]. We suggest that HMG-1 cn shuttle between nucleus and cytoplasm, perhaps in response to the nucleus' need for helix destabilizing proteins.

Antigenicity of histones in various chromatins

Antisera specific to purified histone fractions are used to assess the antigenicity of the histones present in chromatin derived from various sources. The results indicate that the antigenicity of the histones present in chromatin is markedly diminished as compared to the antigenicity of the histones free in solution. The antigenicity of histones in chromatins derived from three different tissues of the rat is very similar. The antigenicity of the histones present in chromatin derived from calf thymus is higher than that of the histones present in rat thymus. It is concluded that the major reason for diminished antigenicity of histones in chromatin is that the histones are complexed in the nucleosome conformation and that the antigenic determinants residing in histones in various chromatins are exposed to similar degrees.

Solid phase radioimmunoassay for chromosomal components

This manuscript describes the use of a solid phase radioimmunoassay for serological analysis of chromosomal components. The applicability of this assay for various studies on nonhistone chromosomal proteins, histones, and chromatin subunits is illustrated. By this technique it is possible to detect and quantify nuclear antigens in the nanogram range. The assay has all the inherent sensitivity and precision of radioimmunoassays and, as such, introduces a new, convenient method for serological analyses of chromosomal components. The results presented reconfirm the serological similarity among the HMG (high mobility group) proteins derived from various sources. The amount of HMG proteins present in mononucleosomes purified from calf thymus is similar to that present in mononucleosomes purified from HeLa cells, suggesting that various tissues contain similar amounts of these proteins. Per nucleosome, dinucleosomes and trinucleosomes contain as much HMG-1 protein as mononucleosomes, suggesting that the protein is not exclusively associated with those regions of DNA which have been solubilized by micrococcal nuclease. Part of the antigenic determinants present in HMG-1 forming a complex in the nucleosomal conformation do not interact with antibodies.

Injected histone antibodies interfere with transcription of lampbrush chromosome loops in oocytes of Pleurodeles

Antibodies to calf thymus histone H2B were purified by chromatography on DEAE-cellulose and injected into oocyte nuclei of Pleurodeles waltlii. As shown by indirect immunofluorescence these antibodies cross-reacted strongly with corresponding histones associated with lampbrush chromosomes. Shortly after injection the lateral loops of the chromosomes retracted into the chromomeres and by 3 h postinjection the ‘lampbrush’ appearance was completely lost and the chromosomes appeared in light-microscopic preparations as rod-like structures consisting of longitudinally coalesced chromomeres. In control oocytes injected with non-immune immunoglobulins or antibodies against a ubiquitous transcript-associated protein no morphological alterations of the lampbrush chromosomes could be observed. Electron microscopic spreads of chromosomes prepared at various times after injection of anti-H2B revealed a progressive loss of transcriptional complexes from the loop axes. Finally, higher-order chromatin configurations, like supranucleosomal globules (‘superbeads’) or cable-like chromatin strands 50–60 nm thick predominated, indicating complete transcriptional inactivation of all chromosomal regions. The results indicate that H2B antibodies react specifically with histones associated with the transcribed DNA of lateral loops in their native state. The resulting antigen-antibody complexes seem to inhibit progression of the RNA polymerases along the template, thus causing the premature release of transcripts, a process analogous to the stripping effect of actinomycin D. The demonstration of histones associated with heavily transcribed regions, which are not compacted into nucleosomes but largely extended, supports the current concept that unfolding of nucleosomes to allow transcription of the DNA does not involve dissociation of histones. In contrast, amplified ribosomal RNA genes are unaffected by injected H2B antibodies. This does not necessarily indicate absence of histones from nucleolar chromatin, since we do not know whether it is accessible in vivo to antibodies or whether the histone antigenic determinants are masked by the presence of other proteins. The technique of injecting specific antibodies should be widely applicable when analysing the in vivo distribution of chromosomal components at the electron-microscopic level and when studying complex metabolic processes, like the cleavage and modification of RNA, by selective inhibition of defined enzymic steps.

Serological analysis of species specificity in the high mobility group chromosomal proteins

The non-histone chromosomal protein of the high mobility group (HMG-1) present in mouse liver was purified to homogeneity. Antibodies against this protein as well as pure HMG-1 derived from calf thymus and HMG-E purified from duck erythrocytes were elicited in rabbits. The interaction between the antibodies and the immunogens was measured by passive hemoagglutination and by quantitative microcomplement fixation. Quantitative microcomplement fixation assays revealed that the immunological distance between HMG-1 from calf thymus and HMG-1 from mouse liver and duck erythrocytes was 15. This corresponds to 3% sequence differences. It was estimated that amino acid substitution occurred at about seven positions in the polypeptide chain. Thus, HMG-1 proteins display remarkable evolutionary conservation in their primary sequence, similar to that displayed by histones H4 and H3, suggesting that their biological function is dependent on stringent structural requirements. HMG-E protein is significantly different from both HMG-1 and HMG-2 derived from calf thymus. As such, it is a protein unique to avian erythrocytes.

Antibodies against chromosomal HMG proteins stain the cytoplasm of mammalian cells

Antibodies specific to protein HMG-1 were purified by affinity chromatography on Sepharose columns to which HMG-1 was covalently bound. Immunofluorescence studies with these antibodies reveal that HMG-1 or components which immunologically cross-react with HMG-1 are present in the cytoplasm of Chinese hamster V-79, rat liver TR-12 and bovine trachea EBTr-NBL-4 cells. At selected antibody concentrations, the fluorescence present in the cytoplasm is more intense than that observed in the nucleus. The presence of HMG-1 protein in the cytoplasm of rat liver cells was verified by direct examination of the protein content of selected cytoplasmic fractions. A protein with electrophoretic mobility identical to HMG-1 was detected by electrophoresis on polyacrylamide gels containing either sodium dodecylsulfate or urea. Furthermore, the cytoplasmic extracts yielded a positive complement fixation with anti-HMG-1, while no reaction was obtained with control anti-H1 sera. We suggest that HMG protins, rather than functioning in the nucleus alone, are important structural elements of the entire cell.

Histone localization in polytene chromosomes by immunofluorescence

Polytene chromosomes of Chironomus thummi were treated with antisera elicited by purified calf thymus histone fractions, and the location of each histone type was visualized by the indirect immunofluorescence technique. Each of the antisera produced specific and distinct patterns of fluorescence, suggesting that it is possible to use the indirect immunofluorescence technique to study the in situ organization of each histone in the various regions of the chromosomes. H1 and H2A antisera produced diffuse fluorescence patterns in acetic acid-fixed chromosomes which become more defined in formaldehyde-fixed preparations. Antisera to H2B, H3 and H4, when reacted with either formaldehyde- or acetic acid-fixed chromosomes, produce distinct banding patterns closely resembling the banding of acetoorcein-stained or phase-contrast-differentiated chromosomal preparations. These antisera produce corresponding patterns of fluorescence for each chromosome, suggesting that the overall organization of the histones is similar in the various bands. Because the dense band regions stain more brightly with antihistone sera than the less compacted interband areas, we believe that the number of antigenic sites of chromosome-bound histones is related to the amount of DNA present, and that the accessibility of histone determinants does not differ between the bands and interbands.

Immunological relatedness of high mobility group chromosomal proteins from calf thymus

The non-histone proteins HMG-1, HMG-2, HMG-3, HMB-8, HMG-14, and HMG-17 (Goodwin, G. H., SANDERS, C., and Johns, E. W. (1973) Eur. J. Biochem. 38, 14) were purified from calf thymus. The apparent molecular weights on polyacrylamide gels run in the presence of sodium dodecyl sulfate of the high mobility group (HMB) proteins were determined. Those for HBG-1 and HMG-2 agreed with the molecular weights determined by sedimentation; that for HMG-17 was anomalously high. Antibodies against HMG-1 were elicited in rabbits. The interaction between HMG-1 and anti-HBG-1 was measured by quantitative precipitation and by the microcomplement fixation technique. Quantitative microcomplement fixation assays revealed that the indices of dissimilarity between HMG-1 and HMG-2, HMG-3, HMG-8, HMG-14, and HMG-17 were 2.0, 1.0, 3.8, 10.0, and 6.1, respectively. These correspond to 6%, 0%, 12%, 20%, and 16% sequence difference between HMG-1 and the other five HMG proteins, although the immunological distance between HMG-1 and HMG-14 may be too large to allow a good correlation between the sequence and the immunological reaction. Antibodies to HMB-1 bind to chromatin purified from calf thymus. Therefore, we suggest that the in situ organization of HMG proteins in chromatin and chromosomes may be studied by serological techniques.

Binding of E. coli RNA polymerase to chromatin subunits

Chromatin subunits were prepared from purified rat liver nuclei and the template properties of the nucleosome preparation studied. It was found that: 1) The fundamental template restriction of chromatin (as compared to deproteinized DNA) is retained in the isolated nucleosomes, 2) On the average one molecule of RNA polymerase is bound to one molecule of DNA purified from nucleosomes, 3) The number of RNA polymerase binding sites on chromatin subunits is 6 to 20 times lower than that of the DNA extracted from these subunits, 4) Transcription can proceed through nucleosomes resulting in RNA chains approximately 150 nucleotides long.

Molecular homogeneity of the histone content of HeLa chromatin subunits

Interaction of affinity chromatographically purified antihistone H3 and antihistone H4 with isolated HeLa core particles, followed by separation of unreacted and reacted particles by sedimentation, demonstrates that every core particle contains these histones. Taken together with our previous data indicating the presence of H2B in every nucleosome (Simpson, R. T., and Bustin, M. (1976), Biochemistry 15, 4305), these data lead to the conclusion that each core particle contains two each of the four smaller histones. In contrast to the lack of interference in binding of more than one molecule of antibody to a single species of histone to the core particle, steric hindrance exists when attempts are made to bind both anti-H3 and anti-H4 to core particles.

Lectins as probes of chromatin structure. Binding of concanavalin A to purified rat liver chromatin

Concanavalin A (Con A) binds specifically to rat liver chromatin. The extent of binding is directly proportional to both chromatin and concanavalin A concentration. It is reversible and inhibited by specific sugars for which concanavalin A has a binding site. Scatchard analysis reveals the presence of one type of Con A-binding site, with an apparent dissociation constant of 3 X 10(-7) M. A maximum of 10 pmol of Con A binds to 10 microgram of chromatin, indicating an average of one binding site/1400 base pairs of DNA. To identify the polypeptide chains which contain Con A-binding sites, chromosomal proteins were separated by electrophoresis on polyacrylamide gels containing sodium dodecyl sulfate. Con A receptors were localized by incubating the gel in 125I-Con A and subsequent autoradiography. Three major polypeptide bands which bind Con A were identified among the nonhistone chromosomal proteins. The apparent molecular weights of these glycoproteins are 135,000, 125,000, and 69,000. We suggest that lectins may serve as probes for the study of the organization of specific components in chromatin.

Immunological cross-reaction between calf and Drosophila histones

Antibodies elicited by purified calf thymus histone fractions are used to quantitate the immunological cross-reactions between calf and Drosophila histones. The index of dissimilarity between calf and Drosophila histones are: H4, 1.0; H2B, 1.0; H3, 1.6; H2A, 2.0; H1, 16. These values respectively correspond to 0, 0, 4, 6, and 27% difference in amino acid composition. The differences in amino acid composition assessed by immunological techniques are in agreement with values obtained by amino acid analysis (Alfageme, C. R., Zweidler, A., Mahowald, A., and Cohen, L. H. (1974) J Biol. Chem. 249, 3729-3736 and Oliver, D., and Chalkley, R. (1972) Exp. Cell. Res. 73, 295-302). The strong immunological cross-reaction between calf and Drosophila histones H4, H3, H2A, and H2B leads us to suggest that antibodies elicited against purified histone fractions derived from calf thymus can serve as "universal" reagents for various studies of chromatin-bound histones. The use of standard preparations of antisera will facilitate comparisons of results obtained in different laboratories with various experimental systems.

Histone compostion of chromatin subunits studied by immunosedimentation

Chromatin subunits were prepared from HeLa cells by in situ digestion of nuclear DNA with micrococcal nuclease followed by sucrose gradient sedimentation. These 11S chromosomal particles (nucleosomes) contain a DNA fragment 140--180 base pairs long and an equal mass of histones, H2A, H2B, H3, and h4. nucleosomes were incubated with purified antibodies to histones H2A and H2B and to hemoglobin A, and the resulting complexes were analyzed by ultracentrifugation. Of these, only anti-H2B bound specifically to nucleosomes. When sufficient antibody was present, all (greater than 98%) the nucleosomes sedimented with increased velocities, indicating that all chromosomal particles contain H2B, as suggested by previous electron microscopic studies (Bustin, M., Goldblatt, D., and Sperling, R. (1976), Cell 7, 297). The amount of antibody reacting with H2B in the nucleosome was quantitated by densitometric scanning of gel electrophoresis patterns of the proteins in various nucleosome-anti-H2B complexes separated by sedimentation on isokinetic sucrose gradients. Under conditions where all particles had increased sedimentation velocities, from 1 to 3 IgG molecules are bound to each nucleosome, the ratio increasing from top to bottom of the sedimenting peak. When nucleosomes are thus dispersed on the basis of reaction with anti-H2B, the ratios of H2A to H4 and of (H2B + H3) to H4 are identical (+/- 8%) for all fractions, suggesting that each nucleosome has an identical histone complement, two each of histones H2A, H2B, H3, and H4. Confidence limits for exclusion of other possible octamers are presented. The variation in ratio of bound antibody to nucleosome probably reflects a normal distribution during the titration, although differential exposure of H2B antigenic determinants in several populations of nucleosomes cannot be excluded as an explanation. The method use should be generally applicable to further studies of the composition and function of nucleosomes.

Immunological cross-reactivity of antibodies to a synthetic undecapeptide analogous to the amino terminal segment of carcinoembryonic antigen, with the intact protein and with human sera

A peptide corresponding to the 11 amino acid residues of the NH2-terminal portion in the sequence of carcinoembryonic antigen(CNTHETIC CEA(1-11) peptide was attached by means of a water-soluble carbodiimide reagent to multichain poly(DL-alanine( as well as to bovine serum albumin. Both macromolecular conjugates provoked in rabbit anti-CEA(1-11) peptide antibodies. The specificity of this immunological system and the crossreactivity between the peptide and intact CEA were investigated by two methods--passive hemagglutination and modified bacteriophage inactivation. Hemmagglutination experiments showed that not only anti-CEA(1-11) sera, but also anti-CEA sera, agglutinated CEA(1-11)-coated sheep erythrocytes, and both these reactions were inhibited with CEA(1-11) peptide. In experiments with the chemically modified bacteriophage technique CEA(1-11)-coated phase was efficiently inactivated with antisera against the CEA(1-11) conjugates, and the inactivation reaction could be totally inhibited with the free peptide. The semipure CEA, but not the pure protein, could also inhibit the phage inactivation, even though less efficiently. On the basis of the above results, sera of some cancer patients were tested for their capacity to inhibit the inactivation of CEA(1-11)-coated phage by means of anti-CEA(1-11) antiserum. The results indicate that sera from a large proportion of patients with adenocarcinomas of the digestive tract, pancreas, and breast are capable of inhibiting the above inactivation, whereas most normal sera do not inhibit.

Histone dimers: a fundamental unit in histone assembly

Histone interactions which occur, at moderate ionic strengths, when several types of purified, renatured histones are mixed at equimolar ratios have been studied. The four histones H2A,H2B,H3 and H4 complex and form dimers. Histone H1 does not interact with the other four histone types and does not form dimers. Mixing of single histone species with preformed histone pairs as well as mixing of two different types of histone pairs, leads to exchange of histones among the pairs and formation of dimers. No trimers are formed. The dimers are in equilibrium with high-molecular weight histone structures. The results indicate that histone dimers may serve as a stable intermediate in histone assembly. Because each histone type (except H1) can interact with itself as well as with each of the other three histone types we suggest that each histone type should be considered as an interchangeable subunit of a multichain protein in which the dimer species is the most stable structure.

Histone and DNA detection in swollen spermatozoa and somatic cells, by immunofluorescence

A method of swelling spermatozoa and other cells, which leads to the exposure of nuclear antigens is described. By applying the indirect IFT on these swollen cells with sera containing antibodies to nuclear antigens, and by comparing the results to those obtained in other tests (measuring anti-nuclear antibodies), the following conclusions could be drawn: (a) By swelling human spermatoza, nuclear antigens of the sperm are exposed, and can be used for the detection of antibodies directed against them. (b) Heterlogous antibodies to histones F2al, FIa2 and F3 which can not be detected in the indirect IFT on rat liver cells, become detectable after swelling of these cells. (c) Mature human spermatozoa contain, in addition to double-stranded DNA and protamine, small amounts of histone F2b and F2a2. (d) In mature human spermatozoa histone F1 is absent.

Chromatin structure visualization by immunoelectron microscopy

Antibodies elicited in rabbits by chromatin and by purified histone H2B have been used to study the structure of chromatin by immunoelectron microscopy. Chromatin spread on grids reveals a structure of closely packed spherical particles with an average diameter of 104 A, arranged either in clusters or in linear arrays of beads, some of which have a supercoil-like arrangement. No DNA strings connecting the beads could be observed. Upon antibody binding, the diameter of the particles increases up to 300 A. This size is compatible with a model where one layer of gamma globulin molecules 110 A long encircles a sphere of chromatin 100 A in diameter. The presence of rabbit gamma globulins on the enlarged beads has been verified by the addition of ferritin-labeled goat anti-rabbit gamma globulins. Anti-chromatin sera which react with nonhistone proteins but not with free histones or DNA react with more than 95% of the beads; this suggests that most of the beads contain nonhistone proteins. Since the number of nonhistone proteins is large, it is improbable that each sphere contains a full complement of these proteins. We therefore suggest that the various chromatin spheres contain different types of nonhistone proteins. About 90% of the chromatin spheres reacted with antibodies to histone H2B, suggesting the most of the chromatin beads contain this type of histone.