Thermal Denaturation Studies of Acetylated Nucleosomes and Oligonucleosmes

Abstract

The thermal melting behaviors of control and acetylated mononucleosomes, dinucleosomes and trinucleosomes have been studied. Along each series of oligonucleosomes, the melting profiles change in a manner consistent with the increasing number of nucleosomes. For the control mononuclecrsome, the melting profile exhibits a premelting region at about 61 -64°C and a major cooperative transition at 75-77 "C. The melting profiles of the control dinucleosomes and trinucleosomes show a premelt at 61 -62 "C (similar to that of the nucleosome core) ; an intermediate transition at 73 -74 "C for the dinucleosome and at 76 -77 "C for the trinucleosome and a major cooperative transition at 79-80 "C for the dinucleosome and at 81 -82 "C for the trinucleosome. The major cooperative transition at the hignest melting temperatures in the melting profiles of the mononucleosome, dinucleosome and trinucleosome comes from the melting of the central region of DNA in the nucleosome strongly complexed with the core histones; the premelt region is attributed to two DNA segments per nucleosome which flank this central DNA region and are free or weakly complexed with histones. The origin of the intermediate transition found for the dinucleosomes and trinucleosomes is not fully understood but probably results from the melting of DNA at the entry to and exit from the nucleosome and the linker D N A which are complexed with histones. A very similar pattern of behavior is observed for the acetylated oligonucleosomes. Direct comparison of the melting profiles of acetylated and control mononucleosomes, dinucleosomes and trinucleosoines show that the premelt region is unaffected by histone acetylation whereas the intermediate and major cooperative transitions for the acetylated oligonucleosomes are broader and occur consistently at lower temperatures than for the controls. These differences support proposals that the N-terminal regions of core histones interact within the nucleosome and on linker DNA. Now that we have an outline understanding of the structure of the nucleosome at low resolution [I -31 and of the packing of nucleosomes in extended and supercoiled chromatin [4 -91, attention is directed to the role of histone acetylation on the structure and function of transcriptionally active or competent chromatin. Allfrey et al. [lo] first correlated one of the requirements of transcriptional activity with histone acetylation and this correlation has been found to hold for enhanced transcriptional activity induced by hormones or drugs (see [I I]). Cell cycle studies of histone H4 acetylation show a strong correlation between the behavior of tetraacetylated H4 and transcriptional activity [I 21. Yeast chromatin, which has a very high overall level of transcriptional activity, has been found to contain 63% of diacetylated, triacetylated and tetraacetylated histone H4 [13].There are four sites of reversible acetylation of lysines in histones H2B, H3 and H4 and one site in histone H2A. All of these sites are located in the N-terminal quarters of the...

The ATTCT repeats of spinocerebellar ataxia type 10 display strong nucleosome assembly which is enhanced by repeat interruptions

“…In addition, initiation of replication and transcription is controlled, at least in part, by the degree of local unwinding of nucleosomal DNA (Kowalski et al, 1988;Potaman et al, 2003). This unwinding can be regulated by histone acetylation; increased acetylation results in a more loosely wound structure with reduced thermal melting temperatures (Yau et al, 1982;Thomsen et al, 1991) allowing access of replication or transcription factors. Furthermore, acetylation of histones can effectively induce negative supercoiling (Norton et al 1989) which may enhance DNA unwinding (Kowalski et al, 1988;Potaman et al, 2003).…”

Histone acetylation in chicken erythrocytes. Rates of deacetylation in immature and mature red blood cells

“…If the N-terminal arms of the histones bind to the outside of the nucleosome core as suggested by Van Holde et al (1974), then histone acetylation would weaken histone-DNA interactions, exposing more of the DNA to the nuclear environment. Experiments with hyperacetylated chromatin and core particles demonstrate 1) increased DNAase I accessibility (Simpson, 1978), 2) enhanced chromatin solubility (Nelson et al, 1980), presumably due to an increase in the overall net negative charge on the nucleohistone, 3) only a subtle weakening in core particle structure (Yau et al, 1982;Imai et al, 1986) and 4) only subtle changes in chromatin higher-order structure (McGhee et al, 1983). These results are consistent with the idea that histone hyperacetylation does not drastically alter chromatin structure, but rather plays a role in enhancing the exposure of the DNA to the nuclear environment.…”

Linker histones H1 and H5 prevent the mobility of positioned nucleosomes.

“…HeLa S3 cells were grown as described (23). Long chromatin was prepared from HeLa or chicken erythrocyte nuclei (15) and depleted of very lysine-rich histones by sucrose gradient centrifugation in 600 mM NaCl/0.2 mM EDTA/0.1 mM phenylmethylsulfonyl fluoride/10 mM Tris-HCl, pH 7.4.…”