A highly conserved sequence in H1 histone genes as an oligonucleotide hybridization probe: isolation and sequence of a duck H1 gene

Natural allelic variation of duck erythrocyte histone H1b

In our previous work (J. Palyga, Genetic polymorphisms of histone H1. b in duck erythrocytes. Hereditas 114, 85-89, 1991) we reported a genetic polymorphism of duck erythrocyte histone H1.b. Here, we screened H1 preparations in a two-dimensional polyacrylamide gel to refine the distribution of allelic forms of H1.b in fifteen duck populations. We have revealed that the frequency of H1.b allelic variants was significantly different among many conservative and breeding duck groups. While b(1) and b(3) were common in all populations screened, the allele b(2), with a slightly lower apparent molecular weight, was confined mainly to brown-feathered ducks (Khaki Campbell and Orpington) and descendent lines. The C- and N-terminal peptides released upon cleavage with N-bromosuccinimide and Staphylococcus aureus protease V8 from duck allelic histones H1. b2 and H1.b3, respectively, migrated differently in the gel, probably as a result of potential amino acid variation in a C-terminal domain.

The vertebrate linker histones H1 zero, H5, and H1M are descendants of invertebrate "orphon" histone H1 genes

We investigated the evolutionary history of the divergent vertebrate linker histones H1 zero, H5, and H1M. We observed that the sequence of the central conserved domain of these vertebrate proteins shares characteristic features with histone H1 proteins of plants and invertebrate animals which otherwise never appear in any vertebrate histone H1 protein. A quantitative analysis of 58 linker histone sequences also reveals that these proteins are more similar to invertebrate and plant histone H1 than to histone H1 of vertebrates. A phylogenetic tree deduced from an alignment of the central domain of all known linker histones places H1 zero, H5, and H1M in close vicinity to invertebrate sperm histone H1 proteins and to invertebrate histone H1 proteins encoded by polyadenylated mRNAs. We therefore conclude that the ancestors of the vertebrate linker histones H1 zero, H5, and H1M diverged from the main group of histone H1 proteins before the vertebrate type of histone H1 was established in evolution. We discuss this observation in the general context of linker histone evolution.

A H1 histone gene-specific AC-box-related element influences transcription from a major chicken H1 promoter

In comparing several histone H1 promoters, we have identified a highly conserved sequence element, 5'-TGTGTTA, located approx. 450-480 bp upstream from the cap site. This TG-box is a near perfect inverted repeat of the previously characterized AC-box (5'-AAACACA). The distance between these elements is also highly conserved. We performed transient transfection assays with cat gene reporter constructs which indicated that both the presence and correct position of the TG-box were essential for maximal expression of the chicken 02 H1 promoter. To the best of our knowledge, this study represents the first demonstration of an effect by the TG-box on transcription of a major histone-encoding H1 gene.

Organization and expression of H1 histone and H1 replacement histone genes

The H1 family is the most divergent subgroup of the highly conserved class of histone proteins [Cole: Int J Pept Protein Res 30:433-449, 1987]. In several vertebrate species, the H1 complement comprises five or more subtypes, and tissue specific patterns of H1 histones have been described. The diversity of the H1 histone family raises questions about the functions of different H1 subtypes and about the differential control of expression of their genes. The expression of main type H1 genes is coordinated with DNA replication, whereas the regulation of synthesis of replacement H1 subtypes, such as H1 zero and H5, and the testis specific H1t appears to be more complex. The differential control of H1 gene expression is reflected in the chromosomal organization of the genes and in different promoter structures. This review concentrates on a comparison of the chromosomal organization of main type and replacement H1 histone genes and on the differential regulation of their expression. General structural and functional data, which apply to both H1 and core histone genes and which are covered by recent reviews, will not be discussed in detail.

Genetic polymorphism of histone H1.z in duck erythrocytes

Three different phenotypes of erythrocyte histone H1.z were detected in several lines of duck by using two-dimensional PAGE. Electrophoresis and inheritance data have shown that two co-dominant alleles, z1 and z2, encode two proteins which differ slightly in their apparent molecular masses. Allele z1 was very abundant and was found at a frequency at least 0.94, while allele z2 was very rare and was present at a frequency of less than 0.06. Limited chemical and enzymic cleavages appeared to indicate that the allelic forms of histone H1.z differed in the C-terminal regions of their molecules.

Isolation and characterization of two human H1 histone genes within clusters of core histone genes

Two human H1 histone genes, termed H1.3 and H1.4, were isolated from two cosmid clones. The H1.4 gene is associated with an H2B gene, whereas genes coding for all four core histones are located in the vicinity of the H1.3 gene. This cluster arrangement was found both in the two cosmid clones and on overlapping bacteriophage clones isolated from an EMBL3 library. In continuation of our previous analysis of two human H1 genes, this analysis raises the number of completely sequenced H1 histone genes within clusters of core histone genes to four.

Structure and expression of the human gene encoding testicular H1 histone (H1t)

The gene coding for the human H1t histone, a testis-specific H1 subtype, was isolated from a genomic library using a human somatic H1 gene as a hybridization probe. The corresponding mRNA is not polyadenylated and encodes a 206-amino-acid protein. Sequence analysis and S1 nuclease mapping of the human H1t gene reveals that the 5' flanking region contains several consensus promoter elements, as described for somatic, i.e., S-phase-dependent H1 subtype genes. The 3' region includes the stem-and-loop structure necessary for mRNA processing of most histone mRNAs. Northern blot analysis with RNAs from different human tissues and cell lines revealed that only testicular RNA hybridized with this gene probe.

Repeat peptide motifs which contain beta-turns and modulate DNA condensation in chromatin

In order to understand better the roles of repeating basic peptide motifs in modifying DNA structure, we have synthesized typical repeats found in the C-terminal domain of histone H1 (KTPKKAKKP)2 and in the N-terminal domain of nucleolin (ATPAKKAA)2. By using circular dichroism in conjunction with Raman and Fourier-transform infrared spectroscopies, we demonstrate that the abilities of the two peptides to affect DNA conformation are dramatically different. Whilst the binding of the nucleolin repeat to DNA does not significantly alter its conformation, the binding of H1 repeat induces a very marked DNA condensation, giving rise to a psi(-)-type circular dichroic spectrum. The H1 repeat thus adopts a more rigid beta-turn-containing structure which probably binds to the DNA minor groove as assessed by competition with the drug Hoechst 33258. Unexpectedly, the DNA condensation induced by the H1 repeat is enhanced by the nucleolin repeat which by itself does not promote any alteration in DNA conformation.

Transcription factor USF from duck erythrocytes transactivates expression of the histone H5 gene in vitro by interacting with an intragenic sequence

The duck histone H5 gene contains a 12 base pair (bp) sequence motif within the coding region, which shows homology in 10 out of 12 bp with the consensus sequence of the USF binding site in the Ad2ML-promoter. The functional equivalent of transcription factor USF, partially purified from whole cell extracts of duck erythrocytes (EUSF), was shown to interact with this intragenic sequence. Electrophoretic mobility shift analyses revealed the selective formation of a complex between this protein fraction and the duck H5 gene. Footprint assays with DNase I delineated specific binding to the intragenic sequence outlined above. Moreover this protein fraction, containing EUSF, transactivates the expression of the duck H5 gene in vitro and elimination of the USF-consensus sequence leads to a loss of stimulation but retains the basic transcription of the gene. These results suggest an as yet unknown functional role of EUSF in the expression of the H5 gene of the duck.

Conserved organization of an avian histone gene cluster with inverted duplications of H3 and H4 genes

The organization of histone gene clusters of the duck Cairina moschata was studied in the DNA inserts of two recombinant phage that overlap and feature identical histone gene arrangements but differ in sequence details and in the extent of repetition of an AT-rich motif in one of the nontranscribed spacer regions. These few but substantial differences between otherwise nearly identical histone gene groups suggest that we have independently isolated alleles of the same site of the duck genome or that this gene arrangement occurs (with slight variations) more than once per haploid genome. Within the histone gene cluster described, H3 and H4 genes are duplicated (with inverted orientation), whereas one H1 gene is flanked by single H2A and H2B genes. The arrangement of duck histone genes described here is identical to a subsection of the chicken genome but differs from any other published histone gene cluster.

A major nucleolar protein, nucleolin, induces chromatin decondensation by binding to histone H1

Using circular dichroism to probe the extent of DNA condensation in chromatin, we have demonstrated that a major nucleolar protein, nucleolin can decondense chromatin. By means of various binding assays we show that nucleolin has a strong affinity for histone H1 and that the phosphorylated N-terminal domain, rich in lengthy stretches of acidic amino acids, is responsible for this ionic interaction. Additional experiments clearly demonstrate that nucleolin is unable to act as a nucleosome core assembly or disassembly factor and hence has little affinity for the core histone octamer. We propose that this nucleolar protein induces chromatin decondensation by binding to histone H1, and that nucleolin can therefore be regarded as a protein of the high-mobility-group type.

The H1 and core histone subtypes: differential gene expression and varied primary structures

The patterns of chromosomal proteins reflect in many cases the functional state of the respective cell type. The H1 histone group is particularly important in this respect, since these histones are involved in the higher order chromatin organization above the level of chains of nucleosomes. In mammals, the H1 histone family comprises at least five main subtypes (H1a-H1e), a testicular variant (H1t) and, thirdly, a subtype H1(0), which is found only in terminally differentiated cells. The H1(0) variant is structurally related to the avian red blood cell specific histone H5, which was the basis for our recent isolation of the human H1(0) gene. Changes of H1 histone patterns may be crucial events in modulating local chromatin arrangements, since the formation of higher order chromatin structures depends on a cooperative interaction of the H1 histones. Variations in their patterns can be studied in vivo during several developmental processes (such as spermatogenesis, erythropoiesis, maturation of several cell types) or in vitro in several tumor cell lines upon treatment with several inducers or upon inhibition of cell division. The differential regulation of the individual H1 subtypes is reflected in the gene and mRNA structures coding for the respective proteins. The cell cycle regulated histones are mostly encoded by non-polyadenylated mRNAs, whereas H5 as well as H1(0) mRNA shows a poly(A) tail at its 3' end. In conclusion, gene activity may not only be controlled at the level of RNA polymerases and their regulatory transcription factors. The varied patterns of chromosomal proteins at different stages during development and differentiation suggest that the local or overall organization of chromatin plays an additional role in these regulatory programs. Hence, the analysis of variations in patterns of chromosomal proteins is an integral part of the investigation of gene regulation mechanisms.