Chromatin Structure and Transcription
Chromatin structure and nucleosome subunit were described in Organization of Genetic Material 1. Packaging of DNA as Nucleosomes in Eukaryotes
. Decondensation of large chromosomal domains (coiled and supercoiled) is a prerequisite for transcription This involves the following steps (also consult Organization of Genetic Material 1. Packaging of DNA as Nucleosomes in Eukaryotes
): (i) Some activator proteins
bind and bring about the formation of nucleosome free regions; how these proteins gain access to specific DNA sequences in chromatin is not known, but non-histone proteins may help in this process. The amino-terminal regions of H3 and H4 may also undergo acetylation,
which is correlated with high level of transcription, (ii) In the nucleosome-free region thus generated, additional transcription factors and RNA polymerase bind. Transcription is thus initiated, (iii) RNA poiymerases can Bring about elongation of transcripts through regions of DNA coiled in the nucleosomes. Histones may be dislodged in this process.