The Crystal Structure Of H2A

One of the main conclusions drawn from this experiment was that the cis memory system is the one used to inherit modified histones because they concluded that epigenetic memory is stored locally in FLC gene. One of the main pieces of evidence to support this is in Figure 3 of this paper. This figure describes heritable expression states, and it is concluded that the cis memory system is used because mitotic stability of all four possible combinations (ON/ON, ON/OFF, OFF/ON, and OFF/OFF) are observed. ‘Mixed’ ON/OFF and OFF/ON states are only seen in cis systems, thus the trans system cannot be implemented. Using this they were also able to show that two identical DNA sequences can have different transcriptional states in the same nucleus, which is only demonstrated by cis memory. Another conclusion they were able to make was that PRC2 is necessary for histone

Clearly, it performs a significant role in the development of the organism on multiple levels. Chromatin directs the course of a cell’s specialization from the time the zygote divides, resulting in the physical structure of a multicellular organism. Evolutionary development is also impacted when an altered form of the chromatin is inherited by the offspring of an organism. Regulation of the chromatin at the level of transcription also provides much insight to the maintenance of the genetic materials, which determines its expression during growth and

Apart from PTMs of the H3 nucleosomes, the centromere code is also unique because CENP-A nucleosomes also undergo PTMs and regulate centromere function (Figure 1). The centromeric histone H4 of CENP-A containing nucleosomes undergo monomethylation at Lysine 20 following deposition of CENP-A into centromeres[94, 95]. When present in the H3 nucleosome, H4K20me1 is associated with transcribed regions throughout the genome[96]. Targeting the H4K20me1-specific demethylase PHF8 to centromeres reduces centromeric level of H4K20me1 and results in reduced recruitment of CENPT and CENP-H[94]. It is not yet clear whether this conserved H4K20me1 is directly responsible for the recruitment of the kinetochore components, or if it is an indirect effect caused by reduced

Out of the many metal hydrides, combination of magnesium hydride with a 7.6wt% storage capacity has sparked the most interest. Using metal hydride to store hydrogen requires an absorption step and a desorption step. Metal hydride is formed by a hydrogen molecule (H2) being adsorbed on the surface, where it is decomposed into individual hydrogen atoms (H). These hydrogen atoms then diffuse into the bulk of the metallic material and finally form a metal

In bacteria and in eukaryotes, the continuing presence of the activator is required to keep the gene on. Scientists argue that active genes often associated with acetylated nucleosomes not because of epigenetic reasons but because of other reasons. One reason is that as genes are transcribed, their nucleosomes are removed and then replaced to make way for RNA polymerase which is involved in transcription. They argue that this nucleosome-replacement machinery works to replace one set of nucleosomes with others that are more highly acetylated. Therefore, nucleosome acetylation accompanies but does not cause transcription. (Ptashne, 2013)

The unique and primary proteins of DNA, the highly basic histone proteins have been found to be ubiquitous and conserved among eukaryotes. DNA and histones co-exist as a closely associated and highly coiled structure. The purpose of such a structural organization is to compact DNA; which would otherwise be too long to be accommodated within the restricted boundaries of a single cell. Core histones (H2A, H2B, H3 and H4) and Linker histones (H1) are the two types that this unique protein is composed of. These Core histone exhibit a structured organization with H2A and H2B forming dimers and H3 and H4 forming tetramers. Along with approximately 146 base pairs of DNA, these core histones form a heterotypic nucleosome complex; weighing about 206

Histones are small, positively charged proteins that interact with negative charged phosphate backbones of DNA. Double-stranded DNA loops around 8 histones (H2A, H2B, H3, and H4) twice, whilst forming the nucleosome, the building block of chromatin packaging (Van Holde et al, 1988). Histones can be modified either by acetylation, phosphorylation, methylation, or ubiquitination (Van Holde et al, 1988). Modifications of the histones collectively influence the compaction of DNA, allowing transcription to recruit histone modifiers for expression or to promote compaction for gene silencing.

At a molecular level, epigenetics variation manifests itself in the way DNA is packaged in the

     Since the beginning of the scientific revolution in the early nineties the mankind looks for

From the above observations, a model for H-NS mediated gene silencing was proposed (Lim et al., 2012a), based on nucleoprotein filament as the basis for gene silencing (Fig I.11). Here, H-NS nucleates at affinity sites in the gene regulatory region and polymerizes to form nucleoprotein filament, which is continuous, encompassing extensive segment of DNA. This might

Cell volume is proportional to the amount of DNA in the cell nucleus. For example, doubling a cell's genome is expected to double the volume of space occupied by the chromosomes in the nucleus, but it causes only a 1.6-fold increase in the surface area of the nuclear envelope. This can disrupt the balance of factors that normally mediate interactions between the chromosomes and nuclear components, including envelope-bound proteins. The peripheral positioning of telomeric and centromeric heterochromatin may be disturbed as well, because there is less relative surface space on the nuclear envelope to accommodate this

Cheutin et al. (2003), observed that the human heterochromatin protein domains were positionally stable in Chinese

Elements are the basic building blocks of matter due to the fact that they are chemically the simplest substances. Whether we can find them in the air or in our gold/silver necklaces, elements are everywhere! One essential element is hydrogen, the first element on the period table (located under Group 1 as an alkaline metal) is composed of a single proton and electron; therefore having an atomic number and atomic mass of 1 and electron configuration of 1s1. In fact, hydrogen is the lightest, simplest and most commonly found chemical element in the universe (it makes up about 90% of the universe by weight). Interestingly enough, the heavier elements on the periodic table were either made from hydrogen or other elements that were made

transcriptionis the first stage of gene expression. Its mechanism is based on rewriting the genetic information contained in the nucleotide sequence of the DNA strand to the RNA. The process can be divided into the initiation, elongation and termination. In a first step, an RNA polymerase binds to the denatured template locally at the site promoter. Then, in elongation step, it adds more ribonucleotides, complementay to the DNA strand, to the nascent mRNA in the 5 '→ 3 '. The process terminates at terminacyjnym, which mostly is characterized by regions complementary to each other, resulting in the formation of secondary structure in a transcript hairpin [5]. In

On the other hand, intermolecular interactions, where a regulator RNA binds to a target RNA via complementary base pairing results in downstream regulatory consequences i.e the formation of the double helix and preventing the binding of protein to target or the formation of the helix itself facilitating binding of proteins like nucleases that in turn degrade the RNA and consequentially affect expression. Alternatively, what can be the case with regulation at the intermolecular level amongst RNA is that the duplex formation might be sequestering a region of the target that would have otherwise taken an alternative secondary structure required for its activity1. Topics in the article will discuss the various forms of RNA found to play key regulatory roles, many of them are involved in key intermolecular interactions that affect expression and hence find implication in human diseases.