Final answer:
Histone repositioning is facilitated by acetylation, deacetylation, histone acetyltransferases (HATs), histone deacetylases (HDACs), and chromatin remodeling complexes, which affect gene transcription by modifying the chromatin structure without changing the DNA sequence.
Step-by-step explanation:
The mechanisms that reposition histones include acetylation, deacetylation, the use of enzyme activities such as histone acetyltransferases (HATs) and histone deacetylases (HDACs), and the action of chromatin remodeling complexes. Acetylation results in a decreased attraction between histones and DNA, loosening the chromatin structure and facilitating transcriptional activation. On the contrary, deacetylation increases the attraction between DNA and histones, leading to tighter chromatin packing and transcriptional repression. Chromatin remodeling complexes actively reposition nucleosomes, altering the exposure of DNA sequences to transcriptional machinery.
Epigenetic changes such as histone acetylation and methylation modify the proteins without altering the underlying DNA sequence, influencing gene expression by changing the chromatin structure. These changes are reversible and important for regulating gene transcription, thus affecting how some genes are silenced while others are activated.