Question

The expression of the BRF1 gene in mice is normally quite low, but mutations in a gene called BRF2 lead to increased expression of BRF1. You feel that nucleosomes are involved in the regulation of BRF1 expression and so you investigate the position of nucleosomes over the TATA box of BRF1 in normal mice and in mice that lack either the BRF2 protein (BRF2-) or part of histone H4 (HHF-) (histone H4 is encoded by the HHF gene). The table pictured summarizes your results. A normal functional gene is indicated by a plus sign (+).

Which of the following conclusion cannot be drawn from your data?
(a) BRF2 is required for the repression of BRF1.
(b) BRF2 is required for the specific pattern of nucleosome positions over the BRF1 upstream region
(c) The specific pattern of nucleosome positioning over the BRF1 upstream region is required for BRF1 repression.
(d) The part of histone H4 missing in HHF- mice is not required for the formation of nucleosomes

Answer 1

The conclusion that cannot be drawn from the provided data is that the part of histone H4 missing in HHF- mice is not required for the formation of nucleosomes, because there's no direct evidence provided in relation to nucleosome formation without this part of histone H4.

Step-by-step explanation:

The question is about the epigenetic regulation of gene expression, specifically the role of nucleosome positioning in regulating the expression of the BRF1 gene in mice, and discerning which conclusion cannot be drawn from the given data. From the provided information, we understand that nucleosomes can move along DNA, affecting gene expression by altering access for transcriptional machinery. Spacing of nucleosomes is therefore critical: closely spaced nucleosomes prevent transcription factor binding, leading to gene repression, while widely spaced nucleosomes permit binding and gene activation. Additionally, the interaction with specific proteins (such as BRF2) and modifications to histone proteins and DNA are also involved in the control of this process.

Nucleosome positioning is associated with the transcriptional activity of genes. In terms of the BRF1 gene, increased expression due to loss of BRF2 or histone H4 alteration implies that these components are normally involved in maintaining a nucleosome arrangement that represses BRF1. However, the concept that the part of histone H4 missing in HHF- mice is not required for the formation of nucleosomes cannot be concluded from the data as there is no information provided regarding the effects of such deletion on nucleosome formation.