Final answer:
A decrease in histone acetyltransferase activity will lead to a greater affinity between histones and DNA, resulting in a lower rate of transcription since tightly packed chromatin inhibits the access of transcription machinery to DNA.
Step-by-step explanation:
Effect of Histone Acetyltransferase Mutations on Histone Affinity and Transcription Rates
If a mutation occurs that causes a decrease in the activity of histone acetyltransferases, the impact would be on the epigenetic regulation mechanisms governing DNA accessibility. Histone acetyltransferases acetylate the lysine residues in histone tails, which diminishes the positive charge on histones, thereby weakening the interaction with the negatively charged DNA backbone. So, if their activity diminishes due to a mutation, histones will most likely have a greater affinity for DNA because the unacetylated histones retain their positive charge, which allows them to bind more tightly to DNA.
Subsequently, the stronger histone-DNA interaction would make it more difficult for the transcription machinery to access the DNA, thereby resulting in a decrease in transcription rates. This is because the tightly packed chromatin state, which is favored when acetylation is reduced, is associated with a repressed gene expression state. Consequently, transcription factors and other proteins essential for transcription cannot easily bind to the necessary DNA sequences. Hence, the correct answer to the question would be (b) greater; a decrease.