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 have a hunch 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). Table Q8-37 summarizes your results. A normal functional gene is indicated by a plus sign (+).

Which of the following conclusions cannot be drawn from your data? Explain your answer.
(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 data is that the part of histone H4 missing in HHF- mice is not required for nucleosome formation, as there is no supporting experimental evidence or literature provided.

Step-by-step explanation:

Among the conclusions based on the provided experimental scenarios, the conclusion that cannot be drawn is (d) The part of histone H4 missing in HHF- mice is not required for the formation of nucleosomes. This statement suggests that histone H4 can be partially missing and nucleosomes can still form, which is not supported by the data provided in the question or known biology literature.

The role of BRF2 in gene regulation is shown by the change in expression levels of the BRF1 gene when BRF2 is not present. Given that BRF1 expression is higher in BRF2- mice, it can be concluded that BRF2 contributes to the repression of BRF1 expression (a).

The specific pattern of nucleosome positioning is associated with the repression of gene expression, presumably because the tightly packed nucleosomes prevent access of transcription factors to the DNA (c), as outlined in the provided figures. Without information about nucleosome formation in HHF- mice, we cannot draw conclusions about the necessity of the missing part of histone H4.