24. After activation of a promoter by the DNA binding activity of a transcription factor, a co-activator is recruited at the region targeted for transcription which in turn creates a binding site for a chromatin remodeling complex. Which one of the following activities of the co-activator is responsible for the recruitment of chromatin remodeling complex?
(1) Histone deacetylase activity.
(2) Histone methyl transferase activity.
(3) Histone acetyl transferase activity.
(4) DNA methyl transferase activity.
Introduction
Activation of gene transcription requires coordinated changes in chromatin structure. After transcription factors bind promoters, co-activators are recruited that modify histones and remodel chromatin to enable transcription. Among co-activator functions, histone acetyltransferase (HAT) activity is crucial for recruiting chromatin remodeling complexes.
Histone Acetylation and Chromatin Remodeling
Histone acetyltransferases add acetyl groups to lysine residues on histone tails, neutralizing their positive charge and loosening DNA-histone interactions. This modification not only relaxes chromatin but also creates docking sites for chromatin remodeling complexes such as SWI/SNF.
These remodeling complexes use ATP to reposition nucleosomes, further enhancing DNA accessibility for the transcription machinery.
Role of Co-activators with HAT Activity
Co-activators like p300/CBP and SRC family proteins possess HAT activity and are recruited to promoters by DNA-bound transcription factors. Their acetylation of histones is an early and essential step that facilitates the subsequent recruitment of remodeling complexes and other co-activators, culminating in robust transcriptional activation.
Conclusion
The histone acetyltransferase activity of co-activators is responsible for recruiting chromatin remodeling complexes to activated promoters. This acetylation-dependent recruitment is a key mechanism by which chromatin structure is dynamically regulated during gene expression.
Answer:
(3) Histone acetyl transferase activity
