Packaging of DNA into chromatin affects all processes on DNA.
Nucleosomes present a strong barrier to transcription, raising important
questions about the nature and the mechanisms of overcoming the barrier.
Recently it was shown that DNA sequence, DNA–histone
interactions and backtracking by RNA polymerase II (Pol II) all contribute
to formation of the barrier. After partial uncoiling of nucleosomal DNA from histone octamer by Pol
II and backtracking of the enzyme, nucleosomal DNA recoils on the octamer,
locking Pol II in the arrested state.
Histone chaperones and transcription factors TFIIS, TFIIF and
FACT facilitate transcription through chromatin using different molecular
mechanisms.
