Chromatin-Modifying Factors and Transcriptional Regulation During Development

摘要: Regulation of gene expression is inherently more complicated in eukaryotes than prokaryotes, because the transcriptional machinery must recognize a chromatin template instead naked DNA. Consequently, chromatin-modifying factors play crucial roles regulation and be involved many biological processes, including ability stem cells to proliferate differentiate into genetically identical but functionally diverse cell types. Although sequence-specific transcription are necessary for downstream target genes, they usually not sufficient RNA polymerase II holoenzyme so large that it cannot access DNA context nucleosomes or higher-order structures; this known as epigenetics. Thus, structure can affect at level individual clusters even whole chromosomes. Cloned embryos sometimes exhibit aberrant patterns methylation CpG dinucleotides abnormal both imprinted nonimprinted genes. Most mammalian occurs cytosines dinucleotides, which symmetrically methylated on complimentary strands Blocking replication does inhibit demethylation, indicates demethylation caused by an yet unidentified demethylase. The maternal genome resistant active paternal becomes accessible demethylases during protamine–to–histone conversion. best-studied type monoallelic imprinting, whereby genes expressed according their parental origin.