Chromatin remodeling factors - These are proteins that enable promoter regions to be able to accept the RNA polymerase complex and bulky machinery depicted in Figure 28.24. Examples of chromatin remodeling factors include the SWI/SNF complex from yeast and the NURF complex from Drosophila. Both require ATP hydrolysis to carry out their task. The two complexes do not seem to remove nucleosomes from the DNA, but rather "open" them in some way.

Another way in which regions of DNA can be transcriptionally activated is by acetylation of specific lysine residues in the N-terminal tails (Figure 28.28) of histones in the nucleosomal core. A number of proteins recruited to the initiation complex by transcriptional activators and TATA binding associated factors TAFs have histone acetylase activity. Acetylation of histones in promoter nucleosomes may help loosen thechromatin structure in these regions.