In order to package the 3x109 nucleotides of DNA into the nucleus, the DNA is wound around histones. These are proteins that bind to the DNA. The interaction of histones and DNA involves:

Methyl and acetyl groupes can be added to the tails of histones.

Genes for histones seem to have no introns.

Histone deacetylases (HDACs) are a group of enzymes closely related to __________. They catalyze acetyl group removal from lysine residues in histones and non-histone proteins, causing transcriptional repression. HDACs are usually components of multiprotein complexes.

以下哪个与基因表达激活有关 (Which of the following is associated with activation of gene expression ?) A: H3K4甲基化 (H3K4 methylation) B: H3K9甲基化 (H3K9 methylation) C: DNA promoter的甲基化 (Methylation of DNA promoter) D: 组蛋白的去乙酰化 (Deacetylation of histones)

Found in the chromatin of all eukaryotic cells, histones have molecular weights between 11,000 and 21,000 and are very rich in the basic amino acids arginine and lysine which together make up about _____ of all the amino acid residues. A: 1/6 B: 1/5 C: 1/4 D: 1/3