Modifications of chromatin structure in control of gene expression

Repetitive sequences in intron and spacer DNA could be sites for binding of chromosomal proteins which maintain chromatin structure and control gene activity. Methylation of DNA guides the binding of acidic nonhistone proteins and maintains the differentiation state during DNA replication. Differentiation inducers modify repressor proteins permitting unfolding of chromatin. Histone H 1 must be removed for gene activity. Phosphorylation of nonhistone proteins probably induces allosteric modifications which permit unfolding of chromatin. Acetylation of nucleosomal histones is necessary to permit passage of RNA polymerase. Deacetylation quickly returns the gene to a normal histone repressed state. Chromosomal RNA attached to nonhistone proteins aids the binding of RNA polymerase to the DNA template. Carcinogens can disrupt normal gene control leading to circumvention of normal cell cycle controls.