sentences:  The regulation of gene expression in eukaryotes is achieved through the interaction of several levels of control that acts both locally to turn on or off individual genes in response to a specific cellular need and globally to maintain a chromatin-wide gene expression pattern that shapes cell identity.Because eukaryotic genome is wrapped around histones to form nucleosomes and higher-order chromatin structures, the substrates for transcriptional machinery are in general partially concealed.Without regulatory proteins, many genes are expressed at low level or not expressed at all.