The primary structure of histone H3 from cycad pollen

The complete primary structure of cycad pollen histone H3 has been established. Microheterogeneity in several positions revealed the presence of H3 variants. Various lysine residues in the N-terminus were found to be completely or partially methylated. The cycad H3 sequence is compared to that of pea and calf.     

The primary structure of histone H3 from the nematode Caenorhabditis elegans

The complete amino acid sequence of histone H3 (135 residues) from the nematode Caenorhabditis elegans has been established. Microheterogeneity occurs at positions 96 and 100 of the chain. The sequences of the nematode H3 isoforms are very similar to the major chain of calf thymus H3 with which they show 4 substitutions in total. The major variant has cysteine in position 96. This is the first report of cysteine in this position in H3 from non-mammalian tissue. An exceptional methylation site has been detected at position 79. Various other sites of secondary modification are of a conservative nature.     

The primary structure of histone H4 from the nematode Caenorhabditis elegans

1. The complete amino acid sequence of histone H4 from the nematode Caenorhabditis elegans has been established. 2. The polypeptide chain consists of 102 amino acids and has a completely alpha-N-blocked serine at residue 1. 3. The sequence differs from vertebrate H4 in position 73 by substitution of cysteine for threonine. 4. Lysine in position 20 is monomethylated.     

The primary structure of a minor isoform (H1.2) of histone H1 from the nematode Caenorhabditis elegans.

The complete amino acid sequence of a minor isoform (H1.2) of histone H1 from the nematode Caenorhabditis elegans was determined. The amino acid chain consists of 190 residues and has a blocked N-terminus. Histone subtype H1.2 is 17 residues shorter than the major isoform H1.1, mainly as the result of deletions of short peptide fragments. Considerable divergence from isoform H1.1 has occurred in the N-terminal domain and the very C-terminus of the molecule, but the central globular domain and most of the C-terminal domain, including two potential phosphorylation sites, have been well conserved. Secondary-structure predictions for both H1 isoforms reveal a high potential for helix formation in the N-terminal region 1-33 of isoform H1.1 whereas the corresponding region in isoform H1.2 has low probability of being found in alpha-helix. No major differences in secondary structure are predicted for other parts of both H1 subtypes. The aberrant conformation of isoform H1.2 may be indicative of a significantly different function.     

The primary structure of the major isoform (H1.1) of histone H1 from the nematode Caenorhabditis elegans.

The complete primary structure of the major isoform (H1.1) of histone H1 from the nematode Caenorhabditis elegans was determined. The amino acid chain consists of 207 amino acids and has a blocked N-terminus. The nematode histone shows rather little sequence identity when compared with proteins of the H1 family derived from other organisms. However, the main characteristic features of H1 molecules have been well conserved: a tripartite domain structure consisting of a central hydrophobic core of about 80 residues, flanked by an N-terminal domain which is somewhat acidic at the very N-terminus, but very basic further on, and a long C-terminal domain very rich in lysine, alanine and proline. Several repeat structures, including a twice (with modification)-repeated and well-conserved phosphorylation site, can be recognized in this region. The presence of O-phosphoserine at these sites could not be demonstrated, however.     

The primary structure of histone H2A from the sperm cell of the sea urchin Parechinus angulosus

The 125 residues of the histone H2A from the sperm cells of the sea urchin Parechinus angulosus have been positioned. The N terminus is blocked by an acetyl group. Compared to the bovine histone, the sea urchin protein differs in 14 positions.     

Nucleosomal structure as probed by H3 histone thiol reactivity

Two H3 histone variants are found in equal amount in HeLa cells, and they have been characterized by two-dimensional gel electrophoresis followed by reaction with specific antibodies. These molecules are the only cysteine-containing histones, and they have been used as the target for thiol-specific reagents, in intact nuclei, isolated nucleosomes, histone complexes, and purified histones. Cysteine residues are available toN-ethylmaleimide only when histones are disassembled from the core particles. Upon reaction with these reagents, one of the H3 variants undergoes profound conformational changes, as revealed by an altered electrophoretic mobility.     

Organization of the histone H3 genes in soybean, barley and wheat

Several variants of the replacement histone H3 genes from soybean, barley and wheat have been cloned and sequenced. Analysis of segregating populations in barley and soybean, as well as analysis of clones isolated from a soybean genomic library, suggested that these genes are dispersed throughout the genome. Several genes contain introns located in similar positions, but of different lengths and sequence. Comparison of mRNA levels in different tissues revealed that the intron-containing and intronless genes have different expression patterns. The distribution of the introns in the histone H3 genes across several plant species suggests that some of the introns might have been lost during the evolution of the gene family. Sequence divergence among introns and gene-flanking sequences in cloned gene variants allowed us to use them as specific probes for localizing individual gene copies and analyzing the genomic distribution of these variants across a range of genotypes.Journal paper No. J-16127 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IowaMention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable     

The structure of ubiquitinated histone H2B.

Ubiquitinated histone H2B (uH2B) has been purified from both calf and pig thymus by exclusion chromatography in 7 M urea. Digestion of uH2B with Staphylococcus aureus V8 protease yielded the peptide 114-125 containing the ubiquitin moiety. Further digestion of this peptide with trypsin removed the ubiquitin and three H2B residues from the N-terminus. Edman degradations of both peptides established that ubiquitin is attached to the epsilon-amino group of lysine 120 in both calf and pig uH2B by an iso-peptide bond to the C-terminal glycine 76 of ubiquitin.     

Polyadenylated H3 histone transcripts and H3 histone variants in alfalfa

Histone H3 mRNAs were found in polyA(+) fractions of total RNA prepared from alfalfa plants, calli and somatic embryos. The sequence analysis of cDNAs revealed the presence of a polyA tail on independent alfalfa H3 mRNAs. A highly conserved sequence motif AAUGAAA identified about 20bp upstream from the 3' ends of the alfalfa H3 cDNAs was suggested to be one of the possible regulatory elements in the 3' end formation and polyadenylation. Three out of the four analysed H3 cDNAs have more than 97% homology with a genomic clone and encode the same protein. While the fourth represents a minor species with only 78.8% homology to the coding region of the genomic clone and encodes a H3 histone with four amino acid replacements. On the basis of compilation analysis we suggest a consensus sequence for plant H3 histones which differs from that of animal's by four amino acid changes.     

Trimethylation of histone H3 lysine 4 impairs methylation of histone H3 lysine 9

Chromatin is broadly compartmentalized in two defined states: euchromatin and heterochromatin. Generally, euchromatin is trimethylated on histone H3 lysine 4 (H3K4^me3) while heterochromatin contains the H3K9^me3 marks. The H3K9^me3 modification is added by lysine methyltransferases (KMTs) such as SETDB1. Herein, we show that SETDB1 interacts with its substrate H3, but only in the absence of the euchromatic mark H3K4^me3. In addition, we show that SETDB1 fails to methylate substrates containing the H3K4^me3 mark. Likewise, the functionally related H3K9 KMTs G9A, GLP, and SUV39H1 also fail to bind and to methylate H3K4^me3 substrates. Accordingly, we provide in vivo evidence that H3K9^me2-enriched histones are devoid of H3K4^me2/3 and that histones depleted of H3K4^me2/3 have elevated H3K9^me2/3. The correlation between the loss of interaction of these KMTs with H3K4^me3 and concomitant methylation impairment leads to the postulate that, at least these four KMTs, require stable interaction with their respective substrates for optimal activity. Thus, novel substrates could be discovered via the identification of KMT interacting proteins. Indeed, we find that SETDB1 binds to and methylates a novel substrate, the inhibitor of growth protein ING2, while SUV39H1 binds to and methylates the heterochromatin protein HP1α. Thus, our observations suggest a mechanism of post-translational regulation of lysine methylation and propose a potential mechanism for the segregation of the biologically opposing marks, H3K4^me3 and H3K9^me3. Furthermore, the correlation between H3-KMTs interaction and substrate methylation highlights that the identification of novel KMT substrates may be facilitated by the identification of interaction partners.